Low temperature plasma deposition process for carbon layer deposition

ABSTRACT

A method of depositing a carbon layer on a workpiece includes placing the workpiece in a reactor chamber, introducing a carbon-containing process gas into the chamber, generating a reentrant toroidal RF plasma current in a reentrant path that includes a process zone overlying the workpiece by coupling plasma RF source power to an external portion of the reentrant path, and coupling RF plasma bias power or bias voltage to the workpiece.

BACKGROUND OF THE INVENTION

High speed integrated circuits formed on a crystalline semiconductorwafer have ultra shallow semiconductor junctions formed by ionimplanting dopant impurities into source and drain regions. Theimplanted dopant impurities are activated by a high temperature annealstep which causes a large proportion of the implanted atoms to becomesubstitutional in the crystalline semiconductor lattice. Such a post-ionimplantation anneal step are done by a rapid thermal process(RTP)-employing powerful lamps that heat the entire wafer volume to avery high temperature for a short time (e.g., a rate-of-rise of about100-200 degrees C. per second and an initial rate-of-fall of 50-100degrees C. per second). The heating duration must be short to avoiddegrading the implanted junction definition by thermally induceddiffusion of the dopant impurities from their implanted locations in thesemiconductor wafer. This RTP approach is a great improvement over theolder post-ion implant anneal technique of heating the wafer in afurnace for a long period of time. RTP using lamps is effective becausethe time response of the heat source (the lamp filament) is short incontrast to the furnace annealing step in which the heater response timeis very slow. The high temperature, short duration heating of the RTPmethod favors the activation of implanted impurities while minimizingthermally induced diffusion.

An improved anneal is done by a flash lamp anneal process employingpowerful flash lamps that heat the surface (only) of the entire wafer toa very high temperature for a very short time (e.g., a fewmilliseconds). The heating duration must be short to avoid degrading theimplanted junction definition by thermally induced diffusion of thedopant impurities from their implanted locations in the semiconductorwafer. This flash approach is an improvement over the RTP approach,because the bulk of the wafer acts as a heat sink and permits rapidcooling of the hot wafer surface. High speed anneal using flashlamps ismore effective because the heating is confined to the surface of thewafer, in contrast to the RTP annealing step in which the entire volumeof the wafer is heated to approximately the same anneal temperature. Theshort duration at high temperature of the flash method minimizesthermally induced diffusion. However, it is difficult to achieve thermaluniformity over the entire wafer. Greater thermal non-uniformity withinwafer creates significant amount of mechanical stress, resulting inwafer breakage and limits the highest operating temperature toapproximately 1150° C. for anneal using flash lamps. The surfacetemperature during flashlamp annealing is determined by the intensityand pulse duration of flashlamps, which are difficult to control in arepeatable manner from one wafer to the next

One problem with RTP is that as device size decreases to 65 nanometers(nm) and below, the minimal thermal diffusion caused by RTP or flashheating becomes significant relative to the device size, despite theshort duration of the RTP or flash heating. Another problem is that thedegree of activation of the implanted dopant impurities is limited bythe maximum temperature of the RTP or flash process. Heating the entirewafer volume in the RTP process above the maximum temperature (e.g.,1100 degrees C.) can create mechanical stresses in the wafer that causelattice defects and wafer breakage in extreme cases. Limiting the wafertemperature to a maximum level (e.g., 1100 degrees C.) prevents suchbreakage, but unfortunately limits the proportion of implanted (dopant)atoms that are activated (i.e., that become substitutional in thesemiconductor crystalline lattice). Limiting the dopant activationlimits sheet conductivity and limits device speed. This problem becomesmore significant as device size is reduced below 65 nm (e.g., down to 45nm).

In order to raise the level of dopant activation beyond that achieved byRTP or flash annealing, laser annealing has been introduced as areplacement for RTP. One type of laser that has been used is a CO2 laserhaving an emission wavelength of 10.6 microns. This laser produces anarrow cylindrical beam, which must be raster-scanned across the entirewafer surface. In order to decrease the surface reflectivity at 10.6microns, the beam is held at an acute angle relative to the wafersurface. Since the CO2 laser wavelength corresponds to a photon energyless than the bandgap of silicon, the silicon must be pre-heated topopulate the conduction band with free carriers in order to facilitatethe absorption of 10.6 micron photons through free carrier absorption. Afundamental problem is that the absorption at 10.6 microns ispattern-dependent because it is affected by the dopant impurities (whichamong other factors, determines the local free carrier concentration),so that the wafer surface is not heated uniformly. Also, conductive ormetallic features on the wafer are highly reflective at the 10.6 micronlaser wavelength, so that this process may not be useful in the presenceof conductive thin film features.

The post-implant anneal step has been performed with short wavelengthpulsed lasers (the short wavelength corresponding to a photon energygreater than the bandgap of silicon). While the surface heating isextremely rapid and shallow, such pulsed lasers bring the semiconductorcrystal to its melting point, and therefore the heating must berestricted to an extremely shallow depth, which reduces the usefulnessof this approach. Typically, the depth of the heated region does notextend below the depth of the ultra-shallow junctions (about 200Angstroms).

The foregoing problems have been overcome by employing an array of diodelasers whose multiple parallel beams are focused along a narrow line(e.g., about 300 microns wide) having a length on the order of the waferdiameter or radius. The diode lasers have a wavelength of about 810 nm.This wavelength corresponds to a photon energy in excess of the bandgapenergy of the semiconductor crystal (silicon), so that the laser energyexcites electron transitions between the valence and conduction bands,which subsequently release the absorbed energy to the lattice and raisesthe lattice temperature. The narrow laser beam line is scannedtransversely across the entire wafer surface (e.g., at a rate of about300 mm/sec), so that each point on the wafer surface is exposed for avery short time (e.g., about 1 millisec). This type of annealing isdisclosed in U.S. Patent Publication No. U.S. 2003/0196996A1 (Oct. 23,2003) by Dean C. Jennings et al. The wafer is scanned much more quicklyby the wide thin beam line than by the pencil-like beam of a singlelaser spot, so that productivity is much greater, approaching that ofRTP. But, unlike RTP, only a small portion of the wafer surface isheated, so that the stress is relieved in the remaining (bulk) portionof the wafer, allowing the peak temperature to be increased above themaximum RTP temperature (e.g., to about 1250-1300 degrees C.). Theentire wafer volume may also be preheated during the laser scanninganneal in order to improve the annealing characteristics. The maximumpreheated temperature is dictated by the technology nodes, processrequirements, compatibility with semiconductor materials, etc. As aresult, dopant activation is much higher, so that sheet resistivity islower and device speed is higher. Each region of the wafer surfacereaches a temperature range of about 1250-1300 degrees C. for about 50microsec. The depth of this region is about 10-20 microns. This extendswell-below the ultra-shallow semiconductor junction depth of about 200Angstroms.

The wafer surface must be heated above a minimum temperature (e.g., 1250degrees C.) in order to achieve the desired degree of activation of theimplanted (dopant) atoms. The elevated temperature is also required toanneal other lattice damage and defects caused by any preceeding implantor thermal steps, in order to improve the electrical characteristics ofthe junctions such as their electrical conductivity and leakage. Thewafer surface must be kept below a maximum temperature (e.g., 1350degrees C.) in order to avoid the melting temperature of thesemiconductor crystal (e.g., crystalline or polycrystalline silicon). Inorder to uniformly heat the entire wafer surface within this desiredtemperature range, the optical absorption of the wafer surface must beuniform across the wafer, and the surface temperature in the illuminatedportion of the wafer surface must be accurately monitored while thelaser beam line is scanned across the wafer (to enable precisetemperature control). This is accomplished by measuring the emission oflight by the heated portion of the wafer surface (usually of awavelength different from that of the laser light source), and themeasurement must be uniformly accurate. As employed in thisspecification, the term “optical” is meant to refer to any wavelength ofa light or electromagnetic radiation emitted from a light source (suchas a laser) that is infrared or visible or ultraviolet or emitted fromthe heated wafer surface.

The problem is that the underlying thin film structures formed on thewafer surface present different optical absorption characteristics anddifferent optical emissivities in different locations on the wafersurface. This makes it difficult if not impossible to attain uniformanneal temperatures across the wafer surface and uniformly accuratetemperature measurements across the wafer surface. This problem can besolved by depositing a uniform optical absorption layer over the entirewafer surface that uniformly absorbs the laser radiation and thenconducts the heat to the underlying semiconductor wafer. Such a filmmust withstand the stress of heating during the laser anneal stepwithout damage or separation, and must be selectively removable afterthe laser anneal step with respect to underlayers and must notcontaminate or damage the underlying semiconductor wafer or thin filmfeatures. Further, the absorber film must attain excellent step coverage(high degree of conformality) over the underlying thin film features.One advantage of such a film is that lateral heat conduction in the filmcan mask non-uniformities in the light beam. This approach has beenattempted but has been plagued by problems. One type of absorber layerconsists of alternating metal and dielectric layers that form ananti-reflective coating. The different layers in this type of absorbermaterial tend to fuse together under the intense heat of the laser beam,and become difficult to remove following the laser anneal step orcontaminate underlying layers with metal.

A better approach used in the present invention is to employ an absorberlayer that can be deposited by plasma enhanced chemical vapor deposition(PECVD). As disclosed in U.S. patent application Ser. No. 10/679,189,filed Oct. 3, 2003 entitled “Absorber Layer for DSA Processing” by LucVan Autryve, et al. and assigned to the present assignee, thePECVD-deposited absorber layer may be amorphous carbon. One advantage ofamorphous carbon is that it is readily and selectively (with respect tounderlayers of other materials) removed by oxidation in a plasma processor a downstream oxidation process employing radicals, at a wafertemperature less than 400C. Another advantage is that carbon isgenerally compatible with semiconductor plasma processes and thereforedoes not involve contamination, so long as excessive implantation doesnot occur. One problem is that the deposited layer is vulnerable tocracking or peeling under the high temperatures of the laser annealstep, unless the layer is deposited at a very high temperature (e.g.,550 degrees C.). (The tendency or resistance to such cracking, peelingor separation of the deposited layer from the underlying layer inresponse to high temperature or high temperature gradients is generallyreferred to in this specification as the thermal or thermal-mechanicalproperties of the deposited layer.) Also the thermal budget (time andtemperature) associated with this PECVD deposition process causeddopants to form clusters which are difficult to dissolve with thesubsequent laser anneal step, particularly for feature sizes below 65 nm(such as feature sizes of about 45 nm). Attempting to solve this problemby reducing the wafer temperature (e.g., to 400 degrees C.) during PECVDdeposition of the absorber layer material creates two problems. First,the thermal properties of the deposited layer are such that it will fail(by cracking, peeling or separation from the wafer) during the laserannealing step. Secondly, the deposited layer that is produced istransparent or has insufficient optical absorption. Another problemencountered with this absorber layer is that it has poor step coverage.We have observed that the PECVD 550 degree absorber layer can have verylarge voids in the vicinity of pronounced steps in the underlying layeror thin film structures sizes below 65 nm.

We feel that failure of the absorber layer (e.g., by peeling orcracking) arises from a lack of high quality chemical bonds (between theunderlying layer and the deposited material) capable of withstanding thestress of being rapidly heated to 1300 degrees C. during the laseranneal step. We feel that, in order to improve the thermal properties ofthe deposited layer, achieving such high quality bonds at low wafertemperature requires high ion energies during the PECVD process. Suchhigh ion energies are not readily attainable in conventional PECVDreactors. We feel that poor step coverage by the absorber layer oramorphous carbon layer is the result of the inability of a conventionalPECVD or HDPCVD reactor to provide an intermediate range of ionization(ion-to-radical ratio) with an adequate level of energetic ionbombardment. These inadequacies arise, in part, because suchconventional PECVD and HDPCVD reactors cannot operate within a wideintermediate range of source power coupling (to generate plasmaelectrons), chamber pressure and wafer voltage. Indeed, the differenttypes of conventional PECVD and HDPCVD reactors tend to operate ateither very high or very low ranges of source power coupling (togenerate plasma electrons), chamber pressure and wafer voltage.Conventional PECVD reactors employ capacitively-coupled RF source powerat relatively high-pressure, resulting in a very low range of ionization(ion-to-radical ratio) with an inadequate level of energetic ionbombardment (and no separate control of voltage or energy). This is dueto the inefficient source power coupling (to generate plasma electrons)and the damping of ion energies by collisions with neutrals at highpressure. Even if separate RF biasing of the wafer is added, the dampingof ion energies by collisions with neutrals at high pressure limits thevoltage and energy range to a low range. Conversely, conventional HDPCVDreactors typically employ inductively-coupled RF source power at verylow pressure. This type of plasma source typically initiates the plasmacapacitively, and then has a high power threshold to transition toinductively coupled power mode. Once the power coupled is above thisthreshold and the source is operating in an inductive mode, the sourcepower coupling is highly efficient and the minimum possible plasmadensity and range of ionization (ion-to-radical ratio) is very high. Theseparate RF wafer bias is coupled to the relatively dense plasma, whichpresents a very low electrical impedance load. The resultant RF biaspower required to produce energetic ion bombardment is very high (>>10kW for >2 kV). High energies are not generally attainable due topractical RF delivery system limitations (RF generators, matchingnetworks, and feed structures). Most of the bias power (e.g., ˜80%) isdissipated as heat on the wafer. It is very difficult to remove the heatat low pressure at an adequate rate to maintain low wafer temperature(<400 deg. C. or lower). Finally, both capacitively-coupled PECVD andinductively-coupled HDPCVD reactors may have power coupling drift (withon-time) issues when used with carbon chemistry when depositingabsorbing or semiconducting films (on RF windows or insulators). Theneed (fulfilled by the toroidal plasma CVD reactor and process describedin detail below) is for a reactor capable of providing ionization ratiosin a wide intermediate range together with an adequate level ofenergetic ion bombardment in all cases, through an ability to operate ina wide intermediate range of source power coupling and level, wafervoltage and chamber pressure. The toroidal plasma CVD reactor does notexhibit power coupling drift when used with carbon chemistry whendepositing absorbing or semiconducting films. This is because thetoroidal plasma CVD reactor is already conducting (metal), having onlyvery thin, isolated DC breaks, which do not accumulate much depositionand are easily in-situ plasma cleaned.

One type of conventional PECVD reactor is a capacitively coupled plasmareactor having a pair of closely-spaced parallel plate electrodes acrosswhich RF plasma source power is applied. Such a capacitively coupledreactor typically is operated at high chamber pressure (2-10 Torr). Highpressure and close-spacing (relative to electrode radius) are employedto maximize deposition rate on the wafer, and to minimize depositionoutside the process region. The plasma source power couples to bothelectrons in the bulk plasma and to ions in the plasma sheaths. Thevoltage across the electrodes is typically relatively low (less than 1KVpp at source power of several kW for 300 mm wafer) and the plasmasheath is very collisional, so that the ion energy is typically low.This type of reactor produces a very low ion-to-neutral population ratioand ion-to-radical ratio, so that the ion flux is low, which probablyincreases the ion energy level or wafer temperature required to obtainthe requisite high quality bonds between the deposited and underlyingmaterials. However, because of the low inter-electrode voltage and thehigh loss of ion energy in the collisional sheath, it is very difficultto generate the ion energy distribution required for high quality bonds.

Another type of conventional PECVD reactor is an inductively coupledhigh plasma density CVD (HPDCVD) reactor in which RF source power isapplied to an inductive antenna. The reactor must be operated at a lowchamber pressure (e.g., 5-10 milliTorr) and high plasma source powerlevel, because of the high minimum induced electric field required tomaintain the inductively coupled plasma mode, which in turn produces ahigh plasma density. The degree of ionization (ratio of ion-to-neutraldensity) produced in this reactor is confined to a range of very highvalues (four or five orders of magnitude greater than that of thecapacitive reactor discussed above), because a large amount of RF sourcepower is required to sustain the inductively coupled mode and becausethe RF induced electric field couples directly to electrons in the bulkplasma. This contrasts with a capacitively coupled plasma in which theRF electric field less efficiently couples to electrons indirectly bydisplacement across the plasma sheath or through plasma sheathoscillations. As a result, plasma density and conductivity is very high,making it difficult to generate a high wafer voltage at practical biaspower levels (since the wafer voltage is loaded down through the highlyconductive plasma). As a result, high ion energies cannot be attainedwithout applying excessive amounts of RF bias power to the wafer. Thiscould overheat the wafer and perhaps destroy the ultra shallow junctiondefinition in the underlying semiconductor crystal lattice (by thermaldiffusion). Typically, for a 300 mm wafer, a wafer voltage of 1-2 kVpeak-to-peak would require RF bias power of about 10 kWatts. Cooling thewafer to maintain ultra-shallow junction definition is difficult at highbias power, and even higher bias voltage (than 1-2 kV) and thus higherpower is desired for best film properties. RF power delivery systems >10kW are very expensive and have limited availability.

Another problem with the HDPCVD reactor is that a large non-conductivewindow must be provided in the chamber ceiling through which the plasmasource power may be inductively coupled from the coil antenna. Thisprevents the use of a conductive showerhead directly overlying thewafer, which limits gas distribution uniformity at the wafer and RF biasground reference uniformity over the wafer. Moreover, coupling of sourcepower into the chamber may be effectively reduced or even blocked if thereactor is employed to deposit a non-insulating material on the wafer,since that same material will also accumulate on the dielectric windowduring processing, creating a conductive shield or semi-conductiveattenuator to the RF power. The temperature of a non-conductive surface,such as the dielectric window of the HDPCVD reactor, cannot beeffectively controlled, so that deposition during processing andpost-process cleaning of the reactor interior is more difficult. Arelated problem in both types of reactors is that plasma source powerseeks a ground return from any available conductive surface in thechamber, so that process control is hampered by electrical changes dueto deposition of by-products on the chamber surfaces. With bothdielectric and metallic materials constituting the chamber surfaces,removal of deposited plasma by-products after processing may bedifficult or may involve undue wear of chamber parts. This may becircumvented by employing disposable shields or process kits to preventdeposition on chamber surfaces. However, such disposable shields cannotprovide good RF ground reference nor be thermally controlled with anyprecision.

In summary, the conventional reactors are either confined to a narrowlow chamber pressure window (in the case of the HDPCVD reactor) or anarrow high chamber pressure window (in the case of the capacitivelycoupled reactor). Neither chamber can achieve a high ion energy, eitherbecause the sheath is highly collisional (in the capacitively coupledreactor) or because the plasma is highly conductive (in the HDPCVDreactor). Also, they are confined to either a narrow highdegree-of-ionization regime (the HDPCVD reactor) or a narrow lowdegree-of-ionization regime (the capacitively coupled reactor).Moreover, both types of reactors are susceptible to wide deviations inperformance whenever they are used for deposition of non-insulatingmaterials, since the accumulation of non-insulating materials acrosselectrode boundaries in a capacitively coupled reactor or on thedielectric window of an inductively coupled reactor will distort orinhibit the coupling of RF source power into the chamber. What is neededis a deposition process carried out at a very low temperature (e.g.,room temperature up to several hundred degrees C.) for forming anoptical absorber layer having such high quality bonds with theunderlying layers (including the semiconductor lattice) that it isimpervious to mechanical failure or separation during the laserannealing step. The process should have a wide source power window, awide degree-of-ionization window in an intermediate range, a wide wafervoltage (bias power) window with wide ion energy window, and a widewafer temperature window.

SUMMARY OF THE INVENTION

A method of depositing a carbon layer on a workpiece includes placingthe workpiece in a reactor chamber, introducing a carbon-containingprocess gas into the chamber, generating a reentrant toroidal RF plasmacurrent in a reentrant path that includes a process zone overlying theworkpiece by coupling plasma RF source power to an external portion ofthe reentrant path, and coupling RF plasma bias power or bias voltage tothe workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a dynamic surface annealing apparatus.

FIG. 2 is a top view of the optics of the apparatus of FIG. 1.

FIG. 3 is an elevational view corresponding to FIG. 2.

FIG. 4 is a broken sectional view of the laser array employed in theapparatus of FIG. 1.

FIG. 5 is a perspective view of a homogenizing light pipe of theapparatus of FIG. 1.

FIG. 6 is a perspective side view of the light pipe of FIG. 5 withcollimating and focusing lenses.

FIG. 7 is a side view corresponding to FIG. 6.

FIG. 8 is a top view corresponding to FIG. 6.

FIG. 9 depicts a toroidal source plasma reactor employed in carrying outa low temperature CVD process.

FIG. 10 is a block diagram depicting a general low temperature CVDprocess performed in the reactor of FIG. 9.

FIG. 11A is a graph illustrating conformality of the layer deposited inthe low temperature process of FIG. 10 as a function of source power.

FIG. 11B is a cross-sectional view of a high aspect ratio opening anddeposited layer that illustrates the definition of conformality.

FIG. 12 is a graph depicting CVD deposition rate as a function of plasmasource power.

FIG. 13 is a graph illustrating the stress of the deposited layer as afunction of bias power level.

FIG. 14 is a block diagram illustrating an embodiment of the process ofFIG. 10.

FIG. 15 is a block diagram illustrating another embodiment of theprocess of FIG. 10.

FIG. 16 is a block diagram of yet another embodiment of the process ofFIG. 10.

FIG. 17 is a cross-sectional view of a thin film structure formed by theprocess of either FIG. 15 or FIG. 16.

FIG. 18 is a graph depicting the implanted ion density as a function ofdepth below the wafer surface in the process of either FIG. 15 or FIG.16.

FIG. 19 is a block diagram illustrating a yet further embodiment of theprocess of FIG. 10.

FIG. 20 is a block diagram of a process for forming ultra-shallowjunctions.

FIG. 21 is block diagram of an alternative embodiment of the process ofFIG. 20.

FIG. 22 is a cross-sectional view of a thin film structure formed in theprocess of FIG. 21.

FIG. 23A is a cross-sectional view of a thin film structure formed inthe process of FIG. 21.

FIG. 23B is a graph of ion implanted species concentration as a functionof depth in the thin film structure of FIG. 23A.

FIG. 24 is a block diagram of an alternative embodiment of the processof FIG. 20.

FIG. 25 is a graph of the additive gas flow rate as a function of timein the process of FIG. 24.

FIG. 26 is a graph of the RF wafer bias voltage as a function of time inthe process of FIG. 24.

FIG. 27 is a cross-sectional view of a thin film structure formed by theprocess of FIG. 24.

FIG. 28 is a block diagram of another alternative embodiment of theprocess of FIG. 20.

FIG. 29A is graph illustrating the proportion of two different additivegases as a function of time in the process of FIG. 24.

FIG. 29B is a graph illustrating the proportion of a single additive gasin another version of the process of FIG. 24.

FIG. 29C illustrates the wafer RF bias power as a function of time inyet another version of the process of FIG. 24.

FIG. 30 depicts a thin film structure having a multi-layered depositedcoating formed by the process of FIG. 24.

FIG. 31 illustrates an operation for annealing ultra-shallow junctionsin the semiconductor wafer.

FIG. 32 illustrates an integrated system for treating a wafer inaccordance with the invention.

FIG. 33 illustrates an integrated system for performing all the stepsentailed in forming ultra-shallow junctions in the surface of a wafer.

DETAILED DESCRIPTION OF THE INVENTION

Introduction:

All the problems mentioned above in the background discussion are solvedby depositing the amorphous carbon optical absorber layer in a lowtemperature PECVD process employing a toroidal source plasma reactor.The toroidal source can be operated with a wide range of ion energy,unlike either the HDPCVD reactor or the capacitively coupled PECVDreactor. Thus, a moderate ion flux can be maintained along with amoderate (or high) ion energy, so that a high quality bond between thedeposited layer and the underlying substrate or thin films isestablished without requiring elevated wafer temperatures. In fact, thewafer temperature may be as cool as room temperature (which minimizesany impact on the implanted ultra-shallow junctions such asrecrystallization of an amorphous layer formed during the implantprocess, dopant cluster formation or thermal diffusion). As a result,the absorber layer formed by this process can withstand the laser beamexposure and extreme heating without separating from the wafer andwithout cracking. The wide bias power or bias voltage range over whichthe toroidal plasma source reactor may be operated enables the stress ofthe deposited layer to be selected within a very wide range, i.e., fromtensile to compressive stress levels. The wide source power range overwhich toroidal plasma source reactor may be operated enables theconformality of the deposited layer to be precisely controlled, forexample, to guarantee a high degree of conformality for excellent stepcoverage. The toroidal source plasma reactor may be operated over a muchwider range of chamber pressure (e.g., 10-80 mT), so that ion densityand plasma sheath collisionality may be controlled over a much widerrange. Since a high ion density is not required, a high wafer voltageand high ion energy may be maintained with a relatively small amount ofbias power (e.g., 7 kV wafer voltage with only 7 kW of bias power for a300 mm wafer). The toroidal plasma source reactor does not require adielectric window for coupling RF power from an inductive antenna intothe chamber (and requires only a very thin dielectric “DC-break”), andtherefore a conductive shower head may be placed at the ceiling. Thisfeature provides the best uniformity of process gas distribution and ahighly uniform low-impedance RF ground reference over the wafer. Becausethere is no requirement for a dielectric window for inductive coupling,virtually the entire chamber can be metal and therefore be thermallycontrolled to regulate deposition during processing and to expeditepost-processing high temperature cleaning of the chamber surfaces. Thetoroidal plasma source generates a plasma with low potential and thetoroidal plasma current requires no ground return through chambersurfaces, so the potential to cause a drift-current out of the processregion is low and therefore there is little or no deposition on chambersurfaces outside of the processing zone. Another advantage of the lackof any need for a dielectric window in the toroidal plasma reactor isthat the reactor may be employed to deposit non-insulating materials onthe wafer without bad effects from accumulation of the non-insulatingmaterial on chamber interior surfaces.

The present invention concerns dynamic surface annealing ofultra-shallow junctions in a semiconductor wafer using an array ofcontinuous wave (CW) diode lasers collimated and focused to a singleknife-edge light beam. The knife-edge light beam is highly intense andis scanned across the wafer in a direction transverse to its length. Thetemperature is raised briefly (to nearly the melting point of silicon)in such a highly localized area about the beam, that its cooling isextremely rapid because of the small volume that is thus heated at anyparticular instant. This technology is described in U.S. PatentApplication Publication No. U.S. 2003/0196996 A1 by Dean C. Jennings etal., published Oct. 23, 2003 (hereinafter referred to as Publication A).At extremely small feature sizes (e.g., 45 nm), it is difficult to heatthe wafer uniformly due to the presence of 3-dimensional topologicalfeatures. These features may be comprised of different materials or havedifferent optical properties. Such features render heat absorptionnon-uniform. They also render the surface emissivity non-uniform, sothat it is impossible to monitor the surface temperature accurately.

These problems have been addressed in the past by depositing an opticalabsorber layer over the entire wafer (which is later removed). Thisabsorber layer has a high imaginary component of the complex refractiveindex (the “k” value of the n+ik, where ‘n’ is the refractive index and‘k’ is the extinction coefficient). A sufficiently thick absorber layermasks emissivity variations due to the underlying films on the wafer, aswell as their dimensional topological features, promoting improved laserabsorption and uniformity of the heat absorption across the wafer (aswell as magnitude and uniformity of surface emissivity). The problem isthat the optical absorber layer must withstand the near-melting pointtemperatures sustained during dynamic surface (laser) annealing, withoutpeeling or separating from the underlying layers. In order to avoid suchpeeling or separation, a high quality bond between the absorber layerand the underlying wafer features is achieved by depositing the absorberlayer at a high temperature. The high temperature also serves to providegood film structural, optical and electrical properties. The problem isthat if the wafer temperature is sufficiently high to achieve a highquality absorber layer that is immune to cracking, peeling orseparation, then the wafer temperature causes the undesirable effects ofeither recrystallizing a pre-existing amorphous silicon layer or causesthe ultra-shallow junctions to diffuse and thereby become poorlydefined, thereby degrading circuit features on the wafer. Lowertemperature conventional CVD absorber layers also have significantlyreduced “k” values, requiring much thicker films to achieve the same netabsorption and immunity to underlayer absorption characteristics.

These problems are overcome in accordance with the invention bydepositing the absorber layer in a low temperature chemical vapordeposition process using the toroidal plasma source low temperature CVDprocess of U.S. Patent Application Publication No. 2004/0200417 byHiroji Hanawa et al., published Oct. 14, 2004 (hereinafter referred toas Publication B). This process employs a unique toroidal source plasmareactor that is described in detail in Publication B. The process iscarried out at very low temperatures, such as under 300 degrees C. oreven as low as room temperature. Thus, it has little or no bad effects(e.g., thermal diffusion or dopant migration, or re-crystallization)upon the ultra-shallow junction features already formed on the wafer. Ifthe absorber layer is to be amorphous carbon, then a carbon-containingprocess gas is employed. In order to enhance absorption of heat from thelaser beam in the absorber layer, the deposited amorphous carbon layeris rendered more opaque by doping it with an impurity such as boron,phosphorous, arsenic, silicon or germanium. This may be done by an ionimplantation step using the toroidal source plasma immersion ionimplantation (P3i) process also described in Publication B, or(alternatively) by incorporating boron into the process gas mixtureduring the CVD low temperature deposition process. Ion implantation ofother impurities (such as nitrogen) into the deposited amorphous carbonabsorber layer may be employed in order to adjust or control thedielectric constant or refractive index of the absorber layer, in orderto obtain a high dielectric constant, for example. Alternatively, otherimpurities (such as nitrogen, hydrogen, oxygen, fluorine) may beincorporated by including them in the process gas mixture during the CVDlow temperature deposition process.

The thermal properties, i.e., the immunity of the low temperaturedeposited absorber layer from peeling, cracking or separation during thedynamic surface laser annealing step, are enhanced by making thedeposited layer a compressively stressed layer. This is accomplished byraising the RF plasma bias power or bias voltage to a relatively highlevel in the low temperature plasma CVD process, as described inPublication B. Excellent step coverage over all the 3-dimensionalmicro-circuit features previously formed on the wafer is obtained bydepositing the absorber layer with relatively high conformality. This isaccomplished by setting the plasma RF source power in the lowtemperature plasma CVD process to a relatively high level, as describedin Publication B. The adhesion of the deposited film may be enhanced bypre-treating the wafer in a cleaning process to remove surface oxidationor other contamination. One pre-treatment process uses a hydrogen plasmagenerated by plasma source power or bias power. A bias voltage may beadded to enhance the cleaning rate. It is believed that the hydrogenions and/or radicals etch the thin oxide or contaminant film. Anotherpre-treatment process uses a nitrogen and/or oxygen plasma generated byplasma source power or bias power. A bias voltage may be added toenhance the cleaning rate. It is believed that the nitrogen and/oroxygen ions and/or radicals etch the thin organic contaminant film. Thispre-treatment process may be followed by the hydrogen plasmapre-treatment process to remove oxidation. Another pre-treatment processuses an inert gas plasma such as helium, neon, argon or xenon to sputterclean the surface oxidation or contamination. Alternatively, a wetpre-treatment process may be used to clean the wafer surface (to enhancebonding) prior to depositing the film.

The absorber layer film optical properties may be tuned with processvariables in order to have a high absorption or extinction coefficientor imaginary part of the complex refractive index at the wavelength ofradiation of the laser light beam and the wavelength of the temperaturemeasurement pyrometer. Such process variables may include impurity(e.g., nitrogen) concentration in the absorber layer, dopant (e.g.,boron) concentration in the absorber layer, wafer temperature, processgas pressure, gas flow rates (of C-containing gas,impurity-containing-gas, dilution gas such as helium, hydrogen orargon), RF bias voltage or power, RF plasma source power, process timeand layer thickness. Additional enhancement of the properties of theabsorber layer may be obtained by grading the concentration of suchimpurities with depth in the layer. This may be accomplished byadjusting the implantation depth profile of impurities that are ionimplanted by the P3i process referred to above, or by ramping theconcentration of such impurities in the process gas or changing RF biasvoltage or power or RF plasma source power or pressure during the lowtemperature CVD process described in Publication B. Additionalenhancement of the properties of the absorber layer may be obtained bycuring the wafer with deposited absorber layer. Curing may includethermal (time at temperature) or UV exposure or a combination. This mayfurther increase or stabilize the absorption or extinction coefficientor imaginary part of the complex refractive index.

The same toroidal source plasma chamber of Publication B may be employedto perform both the absorber layer deposition using low temperature CVDprocess of Publication B as well as any P3i ion implantation processes(as described in Publication B) of impurities into the absorber layer,so that the wafer need not be transported between different chambers.Moreover, the process chamber of Publication A (that performs the laserbeam dynamic surface anneal (DSA) process) is preferably integrated intothe same tool or platform with the toroidal source plasma reactor ofPublication B, so that the wafer can be coated with the absorber layer(e.g., of amorphous carbon), the absorber layer may be enhanced by P3iion implantation of selected impurities and/or dopants, and the waferthen laser annealed using the DSA laser light source of Publication A,all in the same tool. This reduces risk of contamination of the wafer.Moreover the same toroidal plasma source chamber or a second (dedicated)toroidal source plasma chamber (of the same type described inPublication B) or a different type of plasma chamber may be integratedonto the same tool or platform for removing the absorber layer uponcompletion of the laser anneal DSA process.

A fully integrated process requires the following chambers which areused on a given wafer in the following order: a plasma immersion ionimplantation (P3i) chamber for implanting dopants to form ultra-shallowjunction (USJ) source/drain structures; a resist strip chamber forremoving the USJ structure-defining or patterned photoresist; a wetclean chamber for post resist-strip cleaning; a toroidal source or P3iplasma reactor for performing the low temperature CVD process by whichthe amorphous carbon absorber layer is formed; a chamber containing theDSA multiple laser light source and scanning apparatus; a carbon-stripchamber for removing the absorber layer; and a wet clean chamber forpost-strip cleaning of the wafer. At least two or more of the foregoingchambers may be integrated onto a common platform to reduce waferhandling, reduce contamination and increase productivity.

The absorber layer is preferably amorphous carbon, although othersuitable materials may be chosen instead. The product of the filmthickness and the absorption or extinction coefficient or imaginary partof the complex refractive index at the wavelength of radiation of thelaser light beam of the absorber layer must be sufficient to depositover all the 3-dimensional topological features or micro-circuitstructures on the wafer such that the optical properties of theunderlying materials are masked to the degree required by the absorberlayer. The absorber layer optical properties are selected to maximizeheat absorption from the laser beam. The absorber layer thermal orthermal-mechanical properties are selected to render the absorber layerimmune from peeling, cracking or separation from the underlying waferduring DSA laser annealing despite the near-melting point temperaturesof the process.

The absorber layer maximizes uniform absorption from the laser beam evenin the presence of pronounced 3-dimensional surface topological featureson the wafer. The absorber layer is a good heat conductor and thereforeprovides uniform heat distribution across the locally radiated area ofthe wafer. The uniform surface of the absorber layer renders the surfaceemissivity of the wafer uniform, so that accurate measurements of wafertemperature may be continuously made, for good process control.

The absorber layer as described above may also be advantageously usedfor more conventional annealing techniques, such as RTA (rapid thermalanneal) or “spike” anneal or flashlamp anneal, to improve the magnitudeor uniformity of light absorption, and to reduce across wafer andwafer-to-wafer temperature variation. Such a layer may be used to maskthe variation in the optical properties, including 3-D geometriceffects, of underlayers. In this case, the absorber layerdeposition/implantation is tuned for the desirable optical propertiesacross the spectrum of wavelengths that the filament or arc/gasdischarge light source produces. The heat absorber layer of the presentinvention may also be used in RTA annealing of semiconductor wafershaving 3-dimensional micro-circuit topological features. In such a case,the absorber layer optical properties are adapted to the RTA lightsource. Such devices may include such highly reflective structures assilicon-on-insulator or polysilicon on dielectric structures.

Laser Thermal Flux Annealing Light Source:

The dynamic surface anneal light source referred to above uses CW diodelasers to produce very intense beams of light that strikes the wafer asa thin long line of radiation. The line is then scanned over the surfaceof the wafer in a direction perpendicular to the long dimension of theline beam. One embodiment of the light source is illustrated in theschematic orthographic representation of FIG. 1. A gantry structure 110for two-dimensional scanning includes a pair of fixed parallel rails112, 114. Two parallel gantry beams 116, 188 are fixed together a setdistance apart and supported on the fixed rails 112, 114 and arecontrolled by an unillustrated motor and drive mechanism to slide onrollers, source, or ball bearings together along the fixed rails 112,114. A beam source 120 is slidably supported on the gantry beams 116,118, e.g. suspended below the beams 116, 188 and is controlled byunillustrated motors and drive mechanisms to slide along them. A siliconwafer 40 or other substrate is stationarily supported below the gantrystructure 110. The beam source 120 includes laser light source andoptics to produce a downwardly directed fan-shaped beam 124 that strikesthe wafer 40 as a line beam 126 extending generally parallel to thefixed rails 112, 114, in what is conveniently called the slow direction.Although not illustrated here, the gantry structure further includes aZ-axis stage for moving the laser light source and optics in a directiongenerally parallel to the fan-shaped beam 124 to thereby controllablyvary the distance between the beam source 120 and the wafer 40 and thuscontrol the focusing of the line beam 126 on the wafer 40. Exemplarydimensions of the line beam 126 include a length of 1 cm and a width of100 microns with an exemplary power density of 400 kW/cm².Alternatively, the beam source and associated optics may be stationarywhile the wafer is supported on a stage which scans it in twodimensions.

In typical operation, the gantry beams 116, 188 are set at a particularposition along the fixed rails 112, 114 and the beam source 120 is movedat a uniform speed along the gantry beams 116, 188 to scan the line beam126 perpendicularly to its long dimension in a direction convenientlycalled the fast direction. The line beam 126 is thereby scanned from oneside of the wafer 40 to the other to irradiate a 1 cm swath of the wafer40. The line beam 126 is narrow enough and the scanning speed in thefast direction fast enough that a particular area of the wafer is onlymomentarily exposed to the optical radiation of the line beam 126 butthe intensity at the peak of the line beam is enough to heat the surfaceregion to very high temperatures. However, the deeper portions of thewafer 40 are not significantly heated and further act as a heat sink toquickly cool the surface region. Once the fast scan has been completed,the gantry beams 116, 188 are moved along the fixed rails 112, 114 to anew position such that the line beam 126 is moved along its longdimension extending along the slow axis. The fast scanning is thenperformed to irradiate a neighboring swath of the wafer 40. Thealternating fast and slow scanning are repeated, perhaps in a serpentinepath of the beam source 120, until the entire wafer 40 has beenthermally processed. One example of optics beam source 120,orthographically illustrated in FIGS. 2 and 3, receives laser radiationat about 810 nm from two laser bar stacks 132, one of which isillustrated in end plan view in FIG. 4. Each laser bar stack 132includes 14 parallel bars 134, generally corresponding to a vertical p-njunction in a GaAs semiconductor structure, extending laterally about 1cm and separated by about 0.9 mm. Typically, water cooling layers aredisposed between the bars 134. In each bar 134 are formed 49 emitters136, each constituting a separate GaAs laser emitting respective beamshaving different divergence angles in orthogonal directions. Theillustrated bars 134 are positioned with their long dimension extendingover multiple emitters 136 and aligned along the slow axis and theirshort dimension corresponding to the less than 1-micron p-n depletionlayer aligned along the fast axis. The small source size along the fastaxis allows effective collimation along the fast axis. The divergenceangle is large along the fast axis and relatively small along the slowaxis.

Returning to FIGS. 2 and 3 two arrays of cylindrical lenslets 140 arepositioned along the laser bars 134 to collimate the laser light in anarrow beam along the fast axis. They may be bonded with adhesive on thelaser stacks 132 and aligned with the bars 134 to extend over theemitting areas 136. The two sets of beams from the two bar stacks 132are input to conventional optics 142. The source beam 158 is then passedthrough a set of cylindrical lenses 162, 164, 166 to focus the sourcebeam 158 along the slow axis before it enters a one-dimensional lightpipe 170 with a finite convergence angle along the slow axis but beingsubstantially collimated along the fast axis. The light pipe 170, moreclearly illustrated in the orthographic view of FIG. 5 acts as a beamhomogenizer to reduce the beam structure along the slow axis introducedby the multiple emitters 136 in the bar stack 132 spaced apart on theslow axis. The light pipe 170 may be implemented as a rectangular slab172 of optical glass having a sufficiently high index of refraction toproduce total internal reflection. It has a short dimension along theslow axis and a longer dimension along the fast axis. The slab 172extends a substantial distance along an axis 174 of the source beam 158converging along the slow axis on an input face 176 is internallyreflected several times from the top and bottom surfaces of the slab172, thereby removing much of the texturing along the slow axis andhomogenizing the beam along the slow axis when it exits on an outputface 178. The source beam 158, however, is well collimated along thefast axis and the slab is wide enough that the source beam 158 is notinternally reflected on the side surfaces of the slab 172 but maintainsits collimation along the fast axis. The light pipe 170 may be taperedalong its axial direction to control the entrance and exit apertures andbeam convergence and divergence. The one-dimensional light pipe canalternatively be implemented as two parallel reflective surfacescorresponding generally to the upper and lower faces of the slab 172with the source beam passing between them.

The source beam output by the light pipe 170 is generally uniform. Asfurther illustrated in the schematic view of FIG. 6, a furtheranamorphic lens set 180, 182 expands the output beam in the slow axisand includes a generally spherical lens to project the desired line beam126 on the wafer 40. The anamorphic optics 180 shape the source beam intwo dimensions to produce a narrow line beam of limited length. In thedirection of the fast axis, the output optics have an infinite conjugatefor the source at the output of the light pipe 170 (although systems maybe designed with a finite source conjugate) and a finite conjugate atthe image plane of the wafer 40 while, in the direction of the slowaxis, the output optics has a finite conjugate at the source at theoutput of the light pipe 170 and a finite conjugate at the image plane.Further, in the direction of the slow axis, the radiation from themultiple laser diodes of the laser bars is homogenized, which isotherwise non-uniform. The ability of the light pipe 170 to homogenizestrongly depends on the number of times the light is reflectedtraversing the light pipe 170. This number is determined by the lengthof the light pipe 170, the direction of the taper if any, the size ofthe entrance aperture 176 and the exit aperture 178 as well as thelaunch angle into the light pipe 170. Further anamorphic optics focusthe source beam into the line beam of desired dimensions on the surfaceof the wafer 40.

FIGS. 7 and 8 are perpendicularly arranged side views along the fast andslow axes respectively showing the light pipe 170 and some associatedoptics. In the direction of the fast axis, the beam from the lasers bars132 is well collimated and not affected by the light pipe 170 oranamorphic optics. On the other hand, in the direction of the slow axis,the input anamorphic optics 162, 164, 166 condense and converge the beaminto the input end of the light pipe 170. The beam exits the light pipe170 with substantially uniform intensity along the slow axis but with asubstantial divergence. The output anamorphic optics 180, 182 expand andcollimate the output beam along the slow axis.

In order to regulate or control the peak wafer temperature, thetemperature of the illuminated portion of the wafer 40 is constantlymonitored by a pyrometry system. The pyrometry system uses the sameoptics used to focus the laser source light on the wafer to directthermal radiation emitted from the illuminated area of the wafer 40 inthe neighborhood of the line beam 126 in the reverse direction to apyrometer 161 schematically shown in FIG. 3. The pyrometer 161 includesan optical detector 163, such as a photodiode, and an optical filter 165blocking the wavelength of the laser light source (e.g., 810 nm). Thepyrometer filter 165 preferably is a narrow passband filter centered ata region of the Plankian blackbody radiation curve which is quicklychanging at the temperature of interest. For example, the pyrometerpassband may be centered at 950 nm, in which case the detector 163 is asilicon photodiode. The optics are generally reciprocal and thus in thereverse direction detect only a small area of the wafer 40 on or verynear to the line beam 126, and optically expands that image to a muchlarger area. The output of the detector 163 is used by a controller 167to control the power to the laser array 132. A filter (not shown) may beplaced in front of the laser array 132 to block any emission it may haveat the pyrometer wavelength (e.g., 950 nm).

The features of the present invention described below may be employedwith other laser types: CO2 gas-lasers; Neodymium YAG lasers (neodymium:yttrium-aluminum-garnet) which may optionally be frequency-doubled;Excimer lasers (a rare-gas halide or rare-gas metal vapor laser emittingin the ultraviolet (126 to 558 nm) that operates on electronictransitions of molecules, up to that point diatomic, whose ground stateis essentially repulsive) with excitation by E-beam or electricdischarge; diode lasers (light-emitting diode designed to use stimulatedemission to form a coherent light output).

Low Temperature CVD Process of the Toroidal Source Plasma Reactor:

FIG. 9 depicts a toroidal source plasma reactor with which a lowtemperature CVD process is carried out. The plasma reactor has acylindrical side wall 10, a ceiling 12 and a wafer contact-coolingelectrostatic chuck 14. A pumping annulus 16 is defined between thechuck 14 and the sidewall 10. Process gases are introduced through a gasdistribution plate 18 (or “showerhead”) forming a large portion of theceiling 12. Optionally, process gases may also be introduced throughside injection nozzles 20 or by other means. The reactor of FIG. 9 has areentrant RF toroidal plasma source consisting of an external reentranttube 22 coupled to the interior of the reactor through opposite sides ofthe sidewall 10 (or, through openings in the ceiling 12 not shown inFIG. 1). An insulating ring 23 provides a D.C. break along the reentranttube 22. The toroidal plasma source further includes an RF powerapplicator 24 that may include a magnetically permeable toroidal core 26surrounding an annular portion of the reentrant tube 22, a conductivecoil 28 wound around a portion of the core 26 and an RF plasma sourcepower generator 30 coupled to the conductive coil through an optionalimpedance match circuit 32. A second external reentrant tube 22′transverse to the first tube 22 is coupled to the interior of thereactor through opposite sides of the sidewall 10 (or, through openingsin the ceiling 12 not shown in FIG. 1). An insulating ring 23′ providesa D.C. break along the second reentrant tube 22′. A second RF powerapplicator 24′ includes a magnetically permeable toroidal core 26′surrounding an annular portion of the reentrant tube 22′, a conductivecoil 28′ wound around a portion of the core 26′ and an RF plasma sourcepower generator 30′ coupled to the conductive coil through an optionalimpedance match circuit 32′. A process gas supply 34 is coupled to thegas distribution plate 18 (or to the gas injectors 20). A semiconductorwafer or workpiece 40 is placed on top of the chuck 14. A processingregion 42 is defined between the wafer 40 and the ceiling 12 (includingthe gas distribution plate 18). A toroidal plasma current oscillates atthe frequency of the RF plasma source power generator 30 along a closedtoroidal path extending through the reentrant tube 22 and the processingregion 42.

RF bias power or voltage is applied to the chuck 14 by an RF bias powergenerator 44 through an impedance match circuit 46. A D.C. chuckingvoltage is applied to the chuck 14 from a chucking voltage source 48isolated from the RF bias power generator 44 by an isolation capacitor50. The RF power delivered to the wafer 40 from the RF bias powergenerator 44 can heat the wafer 40 to temperatures beyond 400 degreesC., depending upon the level and duration of the applied RF plasma biaspower from the generator 44 if no wafer cooling is employed. It isbelieved that about 80% or more of the RF power from the bias powergenerator 44 is dissipated as heat in the wafer 40. The wafer supportpedestal 14 is an electrostatic chuck having an insulative orsemi-insulative top layer or puck 60. A metal (molybdenum, for example)wire mesh or metal layer 62 inside of the puck 60 forms a cathode (orelectrode) to which the D.C. chucking voltage and RF bias voltage isapplied. The puck 60 is supported on a metal layer 64 that rests on ahighly insulative layer 66. A metal base layer 68 may be connected toground. The wafer 40 is electrostatically held on the chuck 14 byapplying a D.C. voltage from the chucking voltage source 48 to theelectrode 62. This induces an opposite (attractive) image charge in thebottom surface of the wafer 40. The effective gap between the twoopposing charge layers is so minimal as a result of the upward chargemigration in the semi-insulator layer 60 that the attractive forcebetween the chuck and the wafer 40 is very large for a relatively smallapplied chucking voltage. The puck semi-insulator layer 60 therefore isformed of a material having a desired charge mobility, so that thematerial is not a perfect insulator. RF bias power or voltage from theRF bias power generator 44 may be applied to the electrode 62 or,alternatively, to the metal layer 64 for RF coupling through thesemi-insulative puck layer 60. Heat is removed from the puck 60 bycooling the metal layer 64. For this reason, internal coolant passages70 are provided within the metal layer 64 coupled to a coolant pump 72and heat sink or cooling source 74. Heat sink 74 may optionally be aheat exchanger which can also furnish heat, if desired, to metal layer64. A very high heat transfer coefficient between the wafer 40 and thepuck 60 is realized by maintaining a very high chucking force. The forcecan be enhanced by providing a polished surface 60 a.

A low-temperature chemical vapor deposition process preferably employsan electrostatic wafer chuck that both serves to couple RF bias power orvoltage to the wafer and removes (or provides) heat to maintain thewafer temperature at the desired level or below a threshold. Morepreferably, the electrostatic chuck is the type described immediatelyabove with reference to FIG. 9 and in greater detail in U.S. patentapplication Ser. No. 10/929,104 filed Aug. 26, 2004 by Douglas A.Buchberger, Jr., et al. and entitled GASLESS HIGH VOLTAGE HIGH CONTACTFORCE WAFER CONTACT-COOLING ELECTROSTATIC CHUCK. The use of theaforementioned electrostatic chuck (with its high heat transfercoefficient) permits operating of the source power at a higher level(i.e., 5 kW per toroidal source) and bias power at a higher level (i.e.,10 kW) while maintaining wafer temperature under 200 degrees C., or evenunder 100 degrees C., if desired. In addition, the chamber pressure ismaintained in a range between about 5 and 200 mtorr that is sufficientlylow to avoid a defective (e.g., flaky) CVD layer without requiring highwafer temperature. The low chamber pressure avoids excessive ionrecombination that would otherwise depress plasma ion density and/or ionenergy below that required to deposit a high quality film withoutheating the workpiece. The maintenance of a moderate plasma ion densityin the process region obviates the need for any heating of the wafer, sothat a high quality CVD film can be deposited at very low temperature(less than 100 degrees C.), unlike the PECVD reactor. The fact that theplasma density is not very high and the plasma source power level neednot be high permits a wide operating range of bias voltage, withoutrequiring excessive bias power levels, unlike the HDPCVD reactor.

The fact that the CVD reaction can be carried out in the toroidal sourcereactor at a low source power level, if desired, implies a large windowin which source power can be varied, from the minimum level up to amaximum level (e.g., about 5 kW per toroidal source). This window issufficiently large to vary the conformality of the CVD deposited layerbetween non-conformal (0.1 conformality ratio) and conformal (>0.5conformality ratio). At the same time, the stress level of the CVDdeposited layer may be varied by varying the plasma bias power orvoltage applied to the wafer between a low level for tensile stress inthe deposited layer (e.g., 500 Watts) and a high level for compressivestress in the deposited layer (e.g., 3 kWatts or higher). As a result,the conformality and stress of each plasma CVD deposited layer areindependently adjusted by adjusting the source and bias power levels,respectively, to different layers which are either conformal ornon-conformal and having either tensile or compressive stress.Non-conformal films are useful for deep trench filling and for creatingremovable layers over photoresist. Conformal layers are useful for etchstop layers and passivation layers. Layers with compressive stressenhance carrier mobility in underlying or adjacent P-channel MOSFETs,while layers with tensile stress enhance carrier mobility in underlyingor adjacent N-channel MOSFETs. The low minimum plasma source power ofthe toroidal source plasma reactor of FIG. 9 and the highly controllableplasma ion density that the reactor provides as source power isincreased follows from the unique reactor structure of the toroidalsource plasma reactor. Plasma source power is applied via a powerapplicator to a reentrant external conduit through which the toroidal RFplasma current circulates (oscillates), so that the source power densityis very low. This feature makes plasma ion density at the wafer surfacehighly controllable and not subject to excessive increases with plasmasource power, in contrast to the HDPCVD plasma reactor (when thetransition to inductive coupling occurs). Moreover, the highly efficientcoupling of the RF source power applicator to the process gases withinthe external reentrant conduit makes the minimum plasma source power forplasma ignition much smaller than a conventional reactor (such as theHDPCVD reactor). The low temperature CVD process solves the problem ofproviding a plasma CVD process for 65 nm or 45 nm or smaller devices(for example) where the device temperature cannot exceed 400 degrees C.for any significant amount of time without destroying the devicestructure. It also permits plasma CVD deposition over photoresist layerswithout disrupting or destroying the underlying photoresist. Thispossibility opens up an entirely new class of processes described belowthat are particularly suited for nm-sized design rules and can becarried out without disturbing photoresist masking on the device.

Post-CVD ion implantation processes can be carried out in the sametoroidal source reactor that was used to perform the low temperature CVDprocess. The post CVD ion implantation processes include processes forenhancing adhesion between an amorphous or polycrystalline CVD depositedlayer and its base layer, for raising the proportion of a species in theCVD layer beyond a stochiometric proportion, for implanting into the CVDlayer a species not compatible with plasma CVD processes, or forimplanting into the CVD layer a species that alters a particularmaterial quality of the layer, such as dielectric constant or stress.

The low temperature plasma CVD process is useful for CVD formation ofsilicon films, silicon nitride films, silicon-hydrogen films,silicon-nitrogen-hydrogen films, and versions of the foregoing filmsfurther containing oxygen or fluorine. The films exhibit excellentquality and excellent thermal properties, being free of cracking,peeling, flaking, etc., despite the very low temperature at which theCVD process is carried out. For application to CMOS devices, passivationlayers are deposited over P- and N-channel devices with compressive andtensile stresses, respectively, using high non-conformality to enableselective etching and photoresist masking and removal, and etch stoplayers with zero (neutral) stress can be deposited over all devices withhigh conformality. Low temperature plasma CVD process is also useful forCVD formation of carbon films.

A low temperature plasma CVD process employing the toroidal reactor ofFIG. 9 is illustrated in FIG. 10. In this process a carbon orcarbon-containing layer is deposited in a toroidal plasma chemical vapordeposition process. The deposited layer may have some of the attributesof an amorphous carbon material, a polymer carbon material, or agraphitic carbon material, for example, and a wide range of electricaland optical properties, depending upon how the process is carried out.In a later portion of this specification, process control of theproperties of the deposited material will be described. A first step(block 6105 of FIG. 10), which is optional, is to coat the interiorsurfaces of the chamber with a passivation layer to prevent or minimizemetal contamination on the wafer. The passivation layer may, forexample, be of the same material as the CVD film that is to be deposited(e.g., a material containing carbon). The passivation coating on thechamber interior surfaces is carried out by introducing a suitableprocess gas mixture (e.g., a carbon-containing gas such as propylene),and applying plasma source power to generate a toroidal RF plasmacurrent, as in the above-described embodiments. This step is carried outuntil a suitable thickness of the passivation material has beendeposited on interior chamber surfaces. Then, a production workpiece orsemiconductor wafer is placed on the wafer support pedestal (block 6107of FIG. 10). Process gases are introduced (block 6109) containing carbonand (optionally) other species such as hydrogen, or nitrogen, forexample. The chamber pressure is maintained at a low or modest level,e.g., from about 5 to about 200 mTorr (block 6111 of FIG. 10). Areentrant toroidal plasma current is generated in the toroidal sourcereactor (block 6113). The toroidal plasma current is produced bycoupling RF plasma source power (e.g., 100 Watts to 5 kW) (block 6113-1of FIG. 10) into each re-entrant external conduit 22, 22′, and applyingRF plasma bias power between 0 and 10 kWatts (block 6113-2 of FIG. 10).The source power is preferably at an HF frequency on the order of 10 MHz(e.g., such as 13.56 MHz), which is very efficient for producing plasmaions. The bias power is preferably at an LF frequency on the order of aMHz (e.g., such as 2 MHz), which is very effective for producing arelatively large plasma sheath voltage for a given amount of bias power.The magnitude of the source power delivered by the RF generators 180 isadjusted to deposit by chemical vapor deposition a film on the waferwith the desired conformality (block 6115). The magnitude of the biaspower or voltage delivered by the RF generator 162 is adjusted so thatthe deposited film has the desired stress, compressive or tensile (block6117 of FIG. 10). The foregoing process is carried out until the desireddeposited film thickness is reached. Thereafter, certain optionalpost-CVD ion implant processes may be performed (block 6119 of FIG. 10).

FIG. 11A is a graph of conformality ratio of the deposited layer(vertical axis) as a function of the applied RF source power (horizontalaxis). As shown in FIG. 11B, the conformality ratio of a layer 6121deposited by a CVD process on a base layer or substrate 6123 is theratio C/D of the thickness C of a vertical section 6121 a of the layer6121 (deposited on a vertical face 6123 a of the base layer 6123) to thethickness D of a horizontal section 6121 b of the layer 6121 (depositedon a horizontal section 6123 b of the base layer 6123). A conformalityratio exceeding 0.5 indicates a highly conformal CVD-deposited film. Aconformality ratio of about 0.1 indicates a non-conformal CVD-depositedfilm. FIG. 11A illustrates how the wide source power window of thetoroidal source reactor of FIG. 9 spans the conformality ratio rangefrom non-conformal (at about 100 Watts source power) to highly conformal(at about 1 kW source power). FIG. 11A shows that the same toroidalsource reactor can be used for plasma CVD deposition of both conformaland non-conformal films. FIG. 12 is a graph illustrating the CVDdeposition rate (vertical axis) as a function of applied source power(horizontal axis). From zero up to 100 Watts of RF source power, noplasma is ignited in the toroidal source reactor of FIG. 9, and thedeposition rate is zero. Starting at about 100 Watts of source power atabout 13.56 MHz with a constant bias voltage of about 5 kV at about 2MHz, the deposition rate starts at about 500 Angstroms per minute (at100 Watts source power) and reaches about 1000 Angstroms per minute (atabout 2 kW of source power). The advantage is that the deposition rateis sufficiently low so that a high quality defect-free CVD film isformed without requiring any heating or annealing to cure defects thatwould otherwise form at high deposition rates (e.g., 5,000 Angstroms perminute). Therefore, the source power of the toroidal plasma reactor(FIG. 9) can be varied anywhere within the range required to switch theconformality ratio between non-conformal and conformal (i.e., from 200Watts to 2 kW) without requiring heating of the wafer, so that the wafercan remain at a low processing temperature, i.e., below 200 or even 100degrees C. The fact that the toroidal plasma reactor source power may beso increased (to attain a high degree of conformality) without causingexcessive CVD deposition rates follows from the structure of thetoroidal source reactor which avoids excessive increases in ion densityin the process region overlying the wafer 120. Such excessive iondensity is avoided in part because each plasma source power applicator(i.e., each core 26, 26′ surrounding a respective reentrant conduit 22,22′ and the corresponding primary winding 28, 28′) applies plasma sourcepower to a section of the reentrant conduit 22, 22′ that is external ofthe reactor chamber defined by the side wall 10 and ceiling 12, and isremote from the process region 42 overlying the wafer 40. Fortunately,the low and therefore highly controllable increase in plasma ion densitywith source power of the toroidal plasma reactor of FIG. 9 isaccompanied by a very low minimal source power for plasma ignition(e.g., only 100 Watts), which results in the wide source power windowspanning the entire conformality range. This minimal source power levelfor plasma ignition is a result of the efficient manner in which thetoroidal source reactor of FIG. 9 generates the toroidal RF plasmacurrent at HF frequencies such as 13.65 MHz.

Another feature of the toroidal plasma reactor of FIG. 9 is the widerange of RF plasma bias (sheath) voltage with which the reactor may beoperated (e.g., from zero to 10 kV). One aspect of this feature isillustrated in the graph of FIG. 13: the bias voltage operating range(horizontal axis of FIG. 13) spans the range of stress in the CVDdeposited film (vertical axis in the graph of FIG. 13), from tensilestress (+1 gigaPascal) to compressive stress (−1 gigaPascal). Suchpost-CVD ion implantation treatments will be described later in thisspecification. The large range in RF plasma bias (sheath) voltage isattained by using a low frequency (LF) plasma bias source, such as a 2MHz RF source. Such a low frequency translates to a high impedanceacross the plasma sheath over the surface of the wafer, with aproportionately higher sheath voltage. Thus, a relatively small amountof plasma bias power (5 kW) can produce a very large sheath voltage (10kV) at the wafer surface. Such a relatively low bias power level reducesthe heating load on the wafer and reduces the heat and electric fieldload on the wafer support pedestal. Of course, the toroidal sourcereactor of FIG. 9 does not require such a large sheath voltage in orderto ignite or sustain a plasma, and the bias power can be reduced wellbelow 5 kW, to zero, if desired, without extinguishing the plasma. Theconformality selection (between non-conformal and highly conformal)illustrated in FIG. 11A and the stress selection (between tensile andcompressive) illustrated in FIG. 13 are performed independently usingthe very wide source power and bias power operating windows of thetoroidal source reactor of FIG. 9. As a result, the toroidal sourcereactor of FIG. 9 performs a low temperature CVD process of FIG. 10 inwhich different layers may be deposited with different selections ofstress (tensile, zero, or compressive) and different selections ofconformality ratio (non-conformal or highly conformal).

FIG. 14 depicts a variation of the process of FIG. 10 in which anadditive species is included in the deposited layer by including itsprecursor gas in the process gas. The first step is to introduce intothe chamber the carbon material precursor gas (e.g., a hydrocarbon orfluorocarbon or fluoro-hydrocarbon or other carbon-containinggas)_(block 6132 of FIG. 14). This process gas may also include speciesthat enhance the toroidal plasma CVD process without necessarily beingadded into the deposited (carbon) layer, such as an inert gas, forexample. A precursor gas of the desired additive species (to be includedin the CVD deposited carbon layer) is introduced into the chamber (block6133 of FIG. 14). The additive species may, for example, be a precursorof boron (B2H6), or nitrogen or hydrogen or sulfur (H2S) or anotherdesired species. Also, the additive species precursor gas may containprecursor gases for two (or more) different additive species, for theirinclusion in the CVD deposited carbon layer. Then, the toroidal plasmaCVD process is carried out in the chamber (block 6134) by performingsteps 6111, 6113, and (optionally) 6115, 6117 of FIG. 10. The relativegas flow rates of the carbon precursor process gas and the additive(e.g., boron) precursor gas will determine the proportion of theadditive species in the CVD deposited carbon layer. FIG. 15 illustratesa variation of the process of FIG. 14, in which only the carbon materialprecursor gas is first introduced (block 6132) before the toroidalplasma CVD process begun (block 6135). The toroidal plasma CVD processis carried out without the additive species precursor gas for asufficient time to deposit a carbon layer devoid of the additive speciesto a desired threshold thickness (block 6135). At this point in theprocess, the additive species precursor gas is introduced into thechamber while continuing the toroidal source CVD process (block 6136) sothat the remaining (upper) portion of the deposited carbon-containinglayer includes the additive species.

FIG. 16 illustrates another variation of the process of FIG. 10 in whichthe post-CVD wafer treatment step of block 6119 is an ion implantationstep. In the process of FIG. 16, the carbon material precursor processgas is introduced into the chamber (block 6132) and the toroidal plasmaCVD process is carried out on the wafer. Thereafter, an ion implantationprocess is performed on the wafer (block 6137) in which a desiredspecies is implanted into the CVD deposited carbon-containing layer. Thedesired species may be the additive species (one or more) which (likeboron) is chemically active to produce certain desired properties in theCVD deposited carbon-containing layer. The desired species may be an ionbombardment species (such as an inert species) that changes theproperties of the CVD deposited carbon-containing layer by ionbombardment damage. In any case, the ion implantation depth profile ofthe implanted species is set to confine the implanted species within theCVD deposited carbon-containing layer. For example, the ion implantationdepth profile or distribution may have its peak value set at or near anintermediate (e.g., middle) depth in the CVD deposited carbon-containinglayer. Or, if it is desired to have an additive-free layer of carboncontacting the base layer (or silicon wafer surface) with an overlyingcarbon layer containing the additive species, then the ion implantationdepth profile may be centered at an upper depth in the CVDcarbon-containing layer so that little or no ion implantation occursbelow the threshold depth. The result of this latter option isillustrated in FIG. 17, which depicts an underlying layer 6140, a bottomcarbon-containing layer 6139 devoid of the additive species and having athreshold thickness, and an overlying carbon-containing layer 6138 thatincludes the additive species. The layered structure of FIG. 17 is alsorealized in the two-phase toroidal plasma CVD process of FIG. 15. FIG.18 depicts the ion implantation depth profile for the step of block 6137of FIG. 16. Essentially, the ion implantation is confined to depthswell-above the underlying (e.g., wafer) surface. This may beaccomplished (optionally) by leaving un-implanted a bottomcarbon-containing layer (the layer 6139 of FIG. 17) by shifting the iondistribution peak away from the bottom surface, as shown in FIG. 18.

FIG. 19 depicts how any of the processes of FIGS. 14, 5 or 16 may bemodified by incorporating a chamber strip or clean step 6141 and achamber seasoning CVD deposition step 6142, which may be performedeither before or after the toroidal plasma CVD process of FIG. 14, 15,or 16. In FIG. 19, the strip and seasoning steps are depicted as beingperformed prior to the toroidal plasma CVD process. First, prior tointroduction of the wafer into the reactor chamber of FIG. 9, a processgas is introduced into the chamber containing species capable ofstripping deposited films from the exposed chamber interior surfaces(block 6141 of FIG. 19). In the processes of FIGS. 14, 15 and 16 thematerials deposited on the interior chamber surfaces consists mainly ofcarbon, so that the cleaning or strip process gas used in the step ofblock 6141 may consist mainly of oxygen, for example. Other oradditional cleaning gas species may include fluorine, for example.Thereafter, the strip or cleaning process gas is removed from thechamber, and a seasoning layer is deposited on the exposed interiorchamber surfaces of the reactor of FIG. 9 (block 6142 of FIG. 19). Thestep of block 6142 is carried out using the same toroidal plasma CVDprocess described above. Specifically, a carbon precursor gas isintroduced as a seasoning layer precursor gas into the chamber and atoroidal plasma is generated in the chamber. This produces a CVDdeposited carbon-containing seasoning layer on the exposed chamberinterior surfaces. If it is desired to enhance the hardness ordurability of this seasoning layer, then fluorine may be included as aspecies of the seasoning layer precursor gas. For example, the seasoninglayer precursor gas may include a fluorocarbon gas or afluoro-hydrocarbon gas. The major component of the seasoning layerprecursor gas may be a hydrocarbon gas. After the seasoning layer hasreached a desired thickness on the interior chamber surfaces, the waferis introduced into the chamber (block 6143 of FIG. 19) and the toroidalplasma CVD process of FIGS. 10, 14, 15 or 16 is carried out (block 6144of FIG. 19).

Deposition of a Carbon Film by the Toroidal Source CVD Process:

The present invention is useful for depositing films such ascarbon-based films of particular optical properties (at UV, infrared andvisible wavelengths, i.e., “optical” wavelengths) or of particularelectrical properties (e.g., in applications where optical propertiesare not of particular interest) such as conductivity or complexpermittivity. Both electrical and optical properties of such films areadjusted to meet the particular need. The present invention is alsouseful for depositing films such as carbon-based films where subsequentstrippability of the deposited carbon-based film layers is required withselectivity with respect to silicon or other underlying layer. Thepresent invention is also useful for depositing films such ascarbon-based films where conformality control is required, for void-freegap fill applications. The present invention is also useful fordepositing films such as carbon-based films where stress control isrequired.

Hydrogen-Carbon Films:

Carbon films of different electrical and optical properties may bedeposited on wafers using the toroidal plasma source reactor of FIG. 1.The process gas is introduced through the gas distribution plate 18 (orthrough side nozzles 20) of FIG. 1. The process gas may be a hydrocarbongas selected from one (or more) of the hydrogen-carbon gases listedearlier in this specification. The RF toroidal plasma current generatedin the chamber from such a gas causes a hydrogen-containing carbonmaterial to be deposited on the surface of the wafer. The film may beessentially pure carbon with only a negligible amount of hydrogen atoms.Generally, however, the proportion of bonded hydrogen atoms issignificant, so that the deposited material is hydrogenated carbon. Theelectrical conductivity of the deposited film may be set within a rangebetween insulative and semiconductive. The optical properties of thedeposited layer for a selected wavelength band may be set within a rangebetween highly absorptive and transparent. The permittivity may beselected to be “real” (i.e., having a small “imaginary” componentrelative to “real” component) with a magnitude within a low to highrange. The permittivity may be selected to have a significant“imaginary” component relative to the “real” component with a magnitudewithin a low to high range. These electrical and optical properties maybe controlled by any one or a combination of some or all of thefollowing actions:

-   -   (1) adjusting the ion bombardment energy at the wafer surface,    -   (2) adjusting the wafer temperature,    -   (3) selecting the hydrogen-carbon gas species of the process gas        (selecting the hydrogen-carbon ratio of the gas),    -   (4) diluting the process gas with hydrogen,    -   (5) diluting the process gas with an inert gas such as helium,        neon, argon or xenon,    -   (6) adjusting the flux of energetic ions (carbon-containing or        other) at the wafer surface relative to the flux of        carbon-containing radical species to the wafer surface,    -   (7) adding to the process gas a precursor additive gas of one        of: (a) a semi-conductivity-enhancing species, (b) a        resistivity-enhancing species;    -   (8) implanting in the deposited carbon layer one of: (a) a        semiconductivity-enhancing species, (b) a resistivity-enhancing        species.

Adjustment of the ion bombardment energy at the wafer surface may bedone by adjusting RF bias power, RF bias voltage or wafer voltage,and/or chamber pressure, while adjustment of the flux of energetic ionsat the wafer surface may be done by adjusting RF plasma source powerand/or chamber pressure and/or dilution gas flow.

Energetic ion flux adjustment: at constant bias voltage and constantpressure, increasing the RF plasma source power increases the flux ofenergetic ions at the wafer surface. Radical flux at the wafer surfacealso increases with source power. However, at lower to moderate pressure(i.e., mtorr pressure to several hundred mtorr), the ratio of energeticion flux relative to radical flux at the wafer still typically increases(but is still much less than unity). Increasing RF plasma source powerat constant bias voltage, while decreasing pressure, further increasesthe ratio of energetic ion flux relative to radical flux at the wafer.At constant source power and bias voltage, diluting the process gas withargon or xenon tends to increase the flux of energetic ions at the wafersurface, while diluting with helium or neon tends to decrease the fluxof energetic ions at the wafer surface. The effect is intensified asratio of dilution gas flow rate with respect to process gas flow rate isincreased. At lower to moderate pressure (i.e., mtorr pressure toseveral hundred mtorr), increasing pressure at constant RF plasma sourcepower and bias voltage increases the flux of energetic ions at the wafersurface.

Ion energy adjustment: at constant RF plasma source power, increasing RFbias power or voltage increases ion bombardment energy at the wafersurface. At constant RF plasma source power and RF bias voltage and atlower to moderate pressure (i.e. mtorr pressure to several hundredmtorr), increasing the pressure decreases ion energy, though the effectis not necessarily large. At constant RF plasma source power and RF biaspower and at lower to moderate pressure (i.e., mtorr pressure to severalhundred mtorr), increasing the pressure decreases ion energy with largereffect, as the bias voltage (at constant bias power) is reduced due tothe loading effect of the higher plasma ion and electron density.

Selecting the hydrogen-carbon gas species of the process gas (selectingthe hydrogen-carbon ratio of the gas) affects the optical and electricalproperties of the deposited material. Decreasing the hydrogen-carbonratio of the gas typically decreases the C:H bonding and increases theC:C bonding, which increases the optical absorption (decreasestransparency) and increases electrical conductivity. It also tends toincrease the “imaginary” component of permittivity relative to “real”component. For example, C3H6 may produce a deposited layer with greateroptical absorption and/or electrical conductivity than CH4, and C4H6 mayprovide a deposited layer with greater optical absorption and/orelectrical conductivity than C3H6. Diluting the process gas(es) withhydrogen affects the optical and electrical properties of the depositedmaterial. Decreasing the hydrogen dilution typically decreases the C:Hbonding and increases the C:C bonding, which increases the opticalabsorption (decreases transparency) and increases electricalconductivity. It also tends to increase the “imaginary” component ofpermittivity relative to “real” component. In addition to the foregoingsteps for adjusting the optical absorption of the deposited carbonmaterial, optical absorption may be enhanced by including certainadditive materials in the deposited material such as boron, nitrogen orsulfur. Any of these materials may be added by including precursor gasessuch as B2H6, N2 or H2S, respectively, in the process gases. Addingmaterial such as boron, nitrogen or sulfur to the process gases alsosubstantially improves the thermal stability of the deposited carbonmaterial, allowing it to be rapidly heated to high temperature (>1400degree C.) without failure.

Material additions can enhance optical absorption, thermal stability,and/or electrical conductivity and/or permittivity of the depositedmaterial. The ratio of hydrogen to boron, nitrogen or sulfur in theadditive gas affects the properties of the deposited layer. Typicallydecreasing the hydrogen-to-other-element ratio of the gas typicallydecreases the C:H bonding and increases the C:C bonding, which increasesthe optical absorption (decreases transparency) and increases electricalconductivity. It also tends to increase the “imaginary” component ofpermittivity relative to “real” component. For higher optical absorptionor electrical conductivity, B5H9 (as compared to B2H6) or N2 (ascompared to NH3) may increase absorption or conductivity to a greaterdegree. B2H6 typically must be diluted (in the gas bottle) due to itshigher reactivity for safety reasons, and is commercially availablediluted with helium, argon, hydrogen or nitrogen. Hydrogen-diluted-B2H6typically provides greater enhancement of optical absorption andelectrical conductivity than does helium-diluted-B2H6.Argon-diluted-B2H6 may provide even greater enhancement of opticalabsorption and electrical conductivity than does helium- orhydrogen-diluted B2H6. Nitrogen-diluted-B2H6 can also provide greaterenhancement of optical absorption and electrical conductivity than doeshelium- or hydrogen-diluted-B2H6, and can provide a synergistic benefitas described below. B5H9 does not require dilution, and has a higherB-to-H ratio than B2H6, so may provide a greater enhancement of opticalabsorption and electrical conductivity than does helium- orhydrogen-diluted-B2H6. The factors mentioned above which increaseconductivity also tend to increase the “imaginary” component ofpermittivity relative to “real” component. Alternatively, the post-CVDion implantation step described above may be performed with one of theabsorption-enhancement species (B, N or S) by implanting that speciesinto the deposited carbon layer. If this post-CVD implantation step iscarried out by plasma immersion ion implantation using the toroidalplasma source reactor of FIG. 1 for example, then the same process gasmay be employed as above (e.g., B2H6, N2 or H2S).

There is a synergistic benefit of adding (a) boron (i.e., B2H6) plus (b)N2 or other form of nitrogen to the basic amorphous carbon precursorhydrocarbon gas (i.e., C3H6). Thermal stability (i.e., the thermalproperties) of the deposited carbon layer is improved at 450 degrees C.and especially higher temperatures. Specifically, the depositedamorphous carbon layer may be laser heated at least to the melting pointof silicon without delamination of the deposited layer, or peeling, etc.This feature (of adding boron and nitrogen) actually reduces thethreshold wafer voltage or threshold ion energy typically required toavoid delamination or peeling. The foregoing feature, for improving thedeposited layer thermal properties, of combining boron and nitrogenadditives in the hydrocarbon gas may be employed when depositing anamorphous carbon layer having particular electrical propertiescontrolled in the manner described above. It may also be employed fordepositing a carbon layer that is not an optical absorber. It isbelieved that adjustment of the properties of the deposited carbon layeris based upon: (1) adjustment of the proportion of bound hydrogen atomsin the carbon layer, that is, proportion of C:H bonds out of the totalatomic bonds in the deposited carbon layer and (2) the length of the C:Cchains and (3) the bonding hybridization of the carbon atoms and therelative concentration of the different bonds, i.e., sp³:sp²:sp¹. It isfurther believed that increasing the ion energy at the wafer surface andincreasing the energetic ion flux at the wafer surface and increasingthe wafer temperature can have the effect of (1) breaking more C:Cchains (to produce shorter ones) and (2) breaking more C:H bonds (toreduce their presence) and forming more C:C bonds and (3) changing thebonding hybridization of the carbon atoms and the relative concentrationof the different bonds, i.e., sp³:sp²:sp¹. By reducing the hydrogencontent in the process gases in the reactor chamber, the number of C:Hbonds formed in the deposited carbon layer is reduced.

Reduction in the length of the C:C chains changes the state of thedeposited material from a soft polymer to a hard amorphous carbon. Witha reduction in the number of C:H bonds in the deposited carbon layer,the electrical conductivity changes from relatively insulative tosemiconductive, while the optical properties change from relativelytransparent to relatively opaque. Thus, the electrical conductivity ofthe deposited carbon layer may be set anywhere within a range betweeninsulative and semiconductive, while its optical properties may be setanywhere within a range between transparent and opaque, in the toroidalplasma CVD process.

The reduction or breaking of C:C bonds and/or C:H bonds by ionbombardment may require very high ion energies (e.g., on the order of100 eV to 1 keV). Polymer carbon (with long polymer chains) tends to beformed at low (less than 100 degrees C.) wafer temperatures. The lengthof the polymer chains is reduced by ion bombardment, even at the lowwafer temperature. Alternatively, the wafer temperature may be increasedduring the toroidal plasma CVD process (e.g., to 400 degrees C.) to keepthe C:C chain length short. The very high ion energy required to modifythe optical and electrical properties of the deposited carbon layer(requiring high RF bias power) has the effect of enhancing adhesion ofthe carbon layer to the underlying wafer or thin film structurespreviously formed on the wafer, by forming high quality atomic bondsbetween the deposited carbon layer and the underlying material. It alsoenhances the resistance of the deposited film to mechanical failure orseparation induced by thermal stress (e.g., very high temperatures), bygenerating compressive stress in the deposited carbon layer. It alsoincreases the mechanical hardness of the film. Applying high biasvoltage (i.e., >1 kV) substantially improves the thermal stability ofthe deposited carbon material, allowing it to be rapidly heated to hightemperature (>1400 degrees C.) without failure. In addition to heatingthe wafer during the toroidal plasma CVD process, an additional methodfor enhancing the optical absorption of the deposited carbon layer is toheat the wafer to about 400 degrees C. after completion of the CVDprocess. It is believed that this step enhances optical absorption bythe same mechanism of breaking up C:H bonds and forming more C:C bondsin the deposited carbon layer and changing the bonding hybridization ofthe carbon atoms and the relative concentration of the different bonds,i.e., sp³:sp²:sp¹.

Adding an inert dilution gas to the hydrogen-carbon precursor gas maymodify the electrical and optical properties of the film. Adding heliumor neon, for example, makes the film more transparent (and moreinsulating), while adding argon or xenon makes the film more opaque (andmore semiconducting). It is believed, for a constant RF source power andRF bias voltage, that the helium addition decreases the ion flux whileadding argon or xenon increases the ion flux. Increasing the energeticion flux tends to decrease the optical transparency and electricalresistivity of the film. The factors mentioned above which increaseconductivity also tend to increase the “imaginary” component ofpermittivity relative to “real” component. Increasing the RF biasvoltage at constant RF source power increases the ion energy of ionsimpinging on the wafer surface, which tends to decrease the opticaltransparency and electrical resistivity of the film. It also tends toincrease the “imaginary” component of permittivity relative to “real”component. Increasing the RF source power at constant RF bias voltageincreases the energetic ion flux to the wafer surface, which tends todecrease the optical transparency and electrical resistivity of thefilm. It also tends to increase the “imaginary” component ofpermittivity relative to “real” component. Increasing the gas pressureat constant RF source power and RF bias voltage increases the energeticion flux to the wafer surface, which tends to decrease the opticaltransparency and electrical resistivity of the film. It also tends toincrease the “imaginary” component of permittivity relative to “real”component.

The conformality of the deposited carbon layer is adjusted by adjustingthe RF plasma source power. Adjusting deposited layer conformality byadjusting source power is described above in this specification. Thestress of the deposited carbon layer is adjusted by adjusting the RFplasma bias power. Adjusting deposited layer stress by adjusting biaspower is described above in this specification.

Fluoro-Carbon Films:

A fluoro-carbon process gas, selected from one of the fluoro-carbongases listed earlier in this specification, may be employed as the CVDprocess gas, instead of a hydrogen-carbon gas, to deposit afluorine-containing carbon layer on the wafer. Such a layer tends to betransparent across a wide band of wavelengths. A fluorine-containingcarbon layer is useful where a very low-dielectric constant is desiredin the deposited carbon layer. It is also useful where a transparentcarbon layer is desired. It is also useful where a highly insulatingcarbon film is desired. It is also useful where a lower permittivity,having a small “imaginary” component relative to “real” component, isdesired. For fluorocarbon film, preferred fluorocarbon gases are C4F6 orC3F6. Other fluorocarbon gases include C2F4, C2F6, C3F8, C4F8 and C5F8.The process may be used to deposit fluoro-hydrocarbon films. Forfluoro-hydrocarbon films, fluoro-hydrocarbon gases such as CH2F2 may beused. Alternatively, the process may be used to deposit a film which isa combination of hydrocarbon and fluorocarbon materials, in which casecombinations of suitable hydrocarbon and fluorocarbon gases may beemployed as the process gas. Such fluorine-containing films may beamorphous or polymer. Such fluorine-containing films tend to betransparent, depending upon the fluorine content. Such films may have avery low dielectric constant, depending upon fluorine content. Filmscontaining both fluorocarbons (or fluoro-hydrocarbons) and hydrocarbonsmay vary between transparent and absorbing depending upon the relativehydrogen and fluorine content.

The properties of the fluorine-containing carbon layer may be controlledin a manner similar to that described above for hydrogen-containingcarbon layers, by controlling the length of carbon-carbon chains and bycontrolling the proportion and type of F:C bonds in the carbon film. Theproperties may be controlled by any one or a combination of some or allof the following actions:

-   -   (1) adjusting the ion bombardment energy at the wafer surface,    -   (2) adjusting the wafer temperature,    -   (3) selecting the fluorine-carbon gas species of the process gas        (selecting the fluorine-carbon ratio of the gas),    -   (4) diluting the process gas with fluorine,    -   (5) diluting the process gas with an inert gas such as helium,        neon, argon or xenon,    -   (6) adjusting the flux of energetic ions (carbon-containing or        other) at the wafer surface relative to the flux of        carbon-containing radical species to the wafer surface,    -   (7) adding to the process gas a precursor additive gas of one        of: (a) a semi-conductivity-enhancing species, (b) a        resistivity-enhancing species;    -   (8) implanting in the deposited carbon layer one of: (a) a        semiconductivity-enhancing species, (b) a resistivity-enhancing        species.

Adjustment of the ion bombardment energy at the wafer surface may bedone by adjusting RF bias power, wafer voltage and/or chamber pressure,while adjustment of the flux of energetic ions at the wafer surface maybe done by adjusting RF plasma source power and/or chamber pressureand/or dilution gas flow.

Energetic ion flux adjustment: at constant bias voltage and constantpressure, increasing the RF plasma source power increases the flux ofenergetic ions at the wafer surface. Radical flux at the wafer surfacealso increases with source power. However, at lower to moderate pressure(i.e., mtorr pressure to several hundred mtorr), the ratio of energeticion flux relative to radical flux at the wafer still typically increases(but is still much less than unity). Increasing RF plasma source powerat constant bias voltage, while decreasing pressure, further increasesthe ratio of energetic ion flux relative to radical flux at the wafer.At constant source power and bias voltage, diluting the process gas withargon or xenon tends to increase the flux of energetic ions at the wafersurface, while diluting with helium or neon tends to decrease the fluxof energetic ions at the wafer surface. The effect is intensified asratio of dilution gas flow rate with respect to process gas flow rate isincreased. At lower to moderate pressure (i.e., mtorr pressure toseveral hundred mtorr), increasing pressure at constant RF plasma sourcepower and bias voltage increases the flux of energetic ions at the wafersurface.

Ion energy adjustment: at constant RF plasma source power, increasing RFbias power or voltage increases ion bombardment energy at the wafersurface. At constant RF plasma source power and RF bias voltage and atlower to moderate pressure (i.e., mtorr pressure to several hundredmtorr), increasing pressure decreases ion energy, though the effect isnot necessarily large. At constant RF plasma source power and RF biaspower and at lower to moderate pressure (i.e., mtorr pressure to severalhundred mtorr), increasing pressure decreases ion energy with largereffect, as the bias voltage (at constant bias power) is reduced due tothe loading effect of the higher plasma ion and electron density. Theconformality of the deposited fluoro-carbon layer is adjusted byadjusting the RF plasma source power. Adjusting deposited layerconformality by adjusting source power is described above in thisspecification. The stress of the deposited fluoro-carbon layer isadjusted by adjusting the RF plasma bias power. Adjusting depositedlayer stress by adjusting bias power is described above in thisspecification.

A combination of a fluorocarbon gas and a hydrogen-carbon gas may beused as the process gas to form a carbon layer containing both fluorineand hydrogen in a desired proportion. This proportion may be used torealize a desired conductivity or absorption in the deposited carbonlayer. The same methods described immediately above for regulating theproportion of C:H and C:F bonds in the individual C:F and C:H depositedmaterials may be used to control the proportion of C:H and C:F bonds inthe combination C:F+C:H deposited carbon material. A carbon layercontaining both hydrogen and fluorine may also be formed by adding anon-fluorocarbon gas containing fluorine to a hydrocarbon gas in aplasma process using the toroidal source. For example, F2 or BF3 or SiF4or NF3 may be added to a hydrocarbon gas. Conversely, a carbon layercontaining both hydrogen and fluorine may also be formed by adding anon-hydrocarbon gas that contains hydrogen to a fluorocarbon gas in aplasma process using the toroidal source. For example, H2 or B2H6 orSiH4 or NH3 may be added to a fluorocarbon gas.

Low Temperature Deposition of an Optical Absorber Layer:

An optical absorber layer (OAL), which may be an amorphous carbon layer(ACL), is deposited using the toroidal plasma source low temperature CVDprocess described above. The process gas that is introduced into thechamber is a carbon-precursor gas if the OAL is an ACL. We havediscovered that absorption in the amorphous carbon material at thewavelength of interest (e.g., 810 nm) can be enhanced by adding impuritymaterials to the carbon. One example of such an impurity material thatrenders amorphous carbon opaque at 810 nm is boron. In such a case, theprocess gas consists of a carbon precursor gas such as propylene (forexample) and a boron precursor gas (such as B2H6) and a diluent gas forthe B2H6, such as hydrogen. Although helium could be used as the diluentgas, we have found that optical qualities of the amorphous carbon layerare enhanced best in the presence of hydrogen.

FIG. 20 is a block diagram of a junction formation process including thelow temperature CVD step of the toroidal plasma source reactor of FIG. 9for forming the optical absorber layer (OAL) followed by a high speedoptical anneal step such as the dynamic surface anneal (DSA) process ofthe light source of FIGS. 1-8. The first step (block 205 of FIG. 20) isto ion implant dopant impurities into a semiconductor material, such ascrystalline silicon. For device geometries smaller than 65 nm, thisdopant ion implantation step defines ultra-shallow junctions in whichthe dopant-implanted regions extend no further than a few hundredAngstroms. The dopant implant step 205 may be carried out with aconventional beam line implanter or, more preferably, using a plasmaimmersion ion implantation (P3i) process employing the type of toroidalsource reactor depicted in FIG. 9, as described in U. S. PatentApplication Publication No. 2004/0200417 by Hiroji Hanawa et al.,published Oct. 14, 2004. The next step (block 210 of FIG. 20) is tocarry out a low temperature chemical vapor deposition process in thetoroidal plasma source reactor of FIG. 9 to form an optical absorberlayer over the wafer. The CVD process of block 201 consists of thefollowing steps. First, the wafer is placed on the electrostatic chuckof the reactor of FIG. 9 (block 211). A process gas is introduced intothe reactor chamber (block 212). The process gas consists of a precursorfor the material of the OAL. For example, if the OAL is to be amorphouscarbon, then the process gas is (or includes) a precursor for carbon.Such carbon precursor gases have been discussed earlier in thisspecification, and can be any one of (or combination of) thecarbon-containing gases listed earlier herein, including methane,acetylene, ethylene, ethane, propylene, propane, ethyl-acetylene,1,3-butadiene, 1-butene, n-butane, pentane, hexane, toluene, methylbenzene or 1-butyne, or other suitable carbon precursors. In the nextstep (block 213), RF plasma source power is applied by the RF generators30, 30′ to generate toroidal plasma currents in the reentrant tubes 22,22′ of FIG. 9. Chucking voltage is applied to the electrostatic chuck toclamp the wafer, providing tight electrical and thermal coupling betweenwafer and electrostatic chuck. The RF source power levels of thegenerators 30, 30′ are set to realize a desired degree of conformalityin the deposited film (block 214). An RF bias voltage may be applied bythe RF generator 44 to the wafer, and its power or voltage level isadjusted to realize the desired stress level in the deposited layer(block 215 of FIG. 20). In this step, the density of the deposited layermay be increased by increasing the compressive stress in the depositedlayer. This requires an increase in the bias power or voltage, asdescribed earlier in this specification with reference to FIG. 13.Preferably, an additive gas is introduced into the chamber which is aprecursor for a species that, when included in the deposited OAL,enhances an optical property of the OAL (block 216). Typically, thisoptical property is absorption or opacity at the wavelength of the DSAlight source (e.g., 810 nm). If the OAL is amorphous carbon, then theenhancing species may be boron, for example, or nitrogen, hydrogen orother examples referred to earlier in this specification. After thedeposition process step is complete, the wafer is dechucked, typicallyby setting the chucking voltage to zero or to a dehucking voltage, thenthe lift pins raise the wafer from the electrostatic chuck, and then theRF source and/or bias power is turned off.

The absorption-enhancing step of block 216 may consist of heating thewafer very briefly (for a matter of seconds or fraction of a minute) toa moderately hot temperature (e.g., 450 degrees C.) (block 216 a). Thisheating step, which may be carried out in a separate reactor afterdeposition of the OAL, may increase the optical k value (extinctioncoefficient) from about 0.3 to 0.36 in some process examples. The OALmay be deposited to a thickness between about 0.25 micron and about 1micron. Upon completion of the OAL deposition process of block 210, thedynamic surface annealing (DSA) process is performed (block 230 of FIG.20). The wafer is placed in a DSA chamber (block 232), and light fromthe array of CW diode lasers is focused to a thin line on the wafer bythe light source of FIGS. 1-8 at a particular wavelength (e.g., 810 nm)(block 234). This line of light is scanned transversely across theentire wafer (block 236). The rapid heating of the wafer in this stephas been previously described in this specification. Upon completion ofthe DSA step of block 230, the OAL is stripped from the wafer (block240). This step may employ a conventional strip chamber consisting of aheated wafer support and an oxygen gas (radical) source. Preferably,however, the strip chamber is a toroidal source plasma reactor of thetype illustrated in FIG. 9, in which the process gas consists of oxygenand/or nitrogen gas is introduced and a plasma is generated with plasmasource power. The wafer may also be heated (with heated wafer chuck orplasma-heated) and/or be biased to improve removal of the OAL oramorphous carbon layer.

The optical absorption-enhancing species may be put into the OAL bypost-CVD ion implantation step, as distinguished from the step of block216 in which they are put into the OAL during the CVD deposition processby including them in the process gas. In such a case, the process ofFIG. 20 is modified as shown in FIG. 21, in which, after completion ofthe low temperature OAL CVD step of block 210 and before the DSA step ofblock 230, a post-CVD ion implantation step 220 is performed in which anoptical absorption-enhancing species (such as Boron) is implanted intothe OAL. For this purpose, a convention beam line ion implanter may beused, or, preferably, a P3i toroidal source plasma reactor (FIG. 9) isemployed in the manner described in the above-reference publishedapplication by Hanawa et al. This step is depicted in FIG. 22, in whicha wafer 251 has an overlying thin film structure 252 that includesdopant-implanted regions. The wafer 251 and thin film structure 252 arecovered by an amorphous carbon OAL 253 formed in the step of block 210.The post-CVD ion implant step of block 220 is carried out byaccelerating ions (e.g., boron ions) into the OAL 253, as indicated inFIG. 22. In order to avoid introducing boron into the previously-formedultra-shallow junctions, it is necessary for the ion implantation depthprofile of the boron to be well-above the bottom of the OAL 253. FIG.23A depicts the semiconductor (silicon) layer or wafer 251 having adopant-implanted region 251 a, the thin film structure 252 and the OAL253. FIG. 23B depicts the ion implantation concentration depth profileof the optical absorption enhancing species within the OAL 253. Theimplanted ion (boron) concentration ramps downwardly with depth andreaches nearly zero above the bottom of the OAL 253, leaving a bottomOAL layer 253 a un-implanted. This feature can have two advantages. Oneis that contamination of the underlying semiconductor layer 251 by theion implanted absorption-enhancing species is prevented by the presenceof the non-implanted bottom OAL layer 253 a. Another is that leaving thebottom OAL layer 253 a pure may enhance the quality or strength of theadhesion or bonding between the OAL and the underlying material. WhileFIG. 23B depicts an implantation profile that is sloped or ramped, theion implantation profile may be made to be sharper, so that the entireimplanted (upper) region of the OAL 253 can have a nearly uniform(rather than ramped) distribution of implanted species as a function ofdepth.

The extinction coefficient or imaginary part of the index of refractionmay be ramped without resorting to ion implantation of theabsorption-enhancing species. For example, the concentration depthprofile of the absorber-enhancing species added to the OAL during theCVD deposition step may be ramped. This is done by modifying the processof FIG. 20 to include a step in which the proportion of theabsorber-enhancing species added in the step of block 216 is ramped orstepped over time during the CVD deposition step. Alternatively, certainprocess parameters (e.g., bias power) may be ramped or stepped over timeduring the CVD deposition step. These modifications are depicted in FIG.24, in which the CVD deposition process of block 210 concludes witheither one (or both) of two steps. The first step (block 261 of FIG. 24)is to ramp over time the gas flow rate into the chamber of theabsorption-enhancing gas precursor species (e.g., B2H6) during the CVDdeposition step of block 210. The other step (block 262 of FIG. 24) isto ramp over time certain process parameters (such as bias power orvoltage) during the CVD deposition step of block 210. Ramping of thebias power or voltage will create a ramped depth distribution ofcompressive stress and therefore of density in the OAL 253. The densityaffects the absorption and therefore ramping the bias voltage will tendramp the absorption characteristic of the OAL as a function of depthwithin the OAL. FIG. 25 is a graph illustrating how the fraction of theabsorption-enhancing species precursor gas in the process gas is rampedupwardly over time (or CVD layer thickness), starting at a minimumthickness T of the bottom OAL layer. FIG. 26 is a graph illustrating howthe wafer bias voltage may be increased over time during the CVDdeposition process of block 210. The bias voltage is not applied until aminimum layer thickness T has been reached. This latter feature has twoadvantages. First, unintended implantation of impurities into theunderlying semiconductor layer is avoided by removing wafer bias voltageat the beginning of deposition when the underlying layer is exposed andunprotected. Secondly, lack of bias voltage on the bottom OAL layerminimizes stress at the OAL/wafer interface, which may help the bondacross this interface and can avoid leaving a history of stress on theunderlying layer after removal of the OAL. FIG. 27 depicts anelevational view of the OAL 253 and the underlying layers 251, 252. TheOAL 253 includes a pure and unstressed bottom layer 253 a, and an upperportion having a compressive stress and an impurity concentration thatincreases with height.

The process of FIG. 20 may be modified so as to enhance opticalabsorption by forming an antireflection coating within the OAL 253. Thisfeature may be employed in combination with or in lieu of any of theforegoing absorption-enhancing process steps. This modification isillustrated in FIG. 28, in which the CVD process 210 concludes with thestep of block 217 of forming successive sub-layers in the OAL ofalternating high-k (opaque) and low-k (transparent) values. The term “k”refers to the extinction coefficient, the imaginary part of the index ofrefraction at the wavelength of the DSA light source (e.g., 810 nm). InFIG. 28, the OAL deposition step of block 210 includes the step of block217 of forming successive sub-layers of the OAL of alternating high andlow values of k at the wavelength of the DSA light source of FIGS. 1-8.This step may include any one of the following steps: (a) step (turn onand off) the absorption-enhancing additive gas flow to the chamber(block 217 a of FIG. 28), (b) alternate the additive gas content betweenan absorption-enhancing additive gas species (e.g., a boron-containinggas) and a transparency-enhancing additive gas species (e.g., afluorine-containing additive gas) (block 217 b of FIG. 28), (c)alternate the CVD process parameters between values that promoteformation of a high k-material and values that promote formation of alow-k material (block 217 c of FIG. 28).

FIG. 29A is a graph illustrating the (additive) absorption-enhancingspecies precursor gas fractional composition of the total process gas inthe reactor chamber as a function of time, which is stepped or pulsed upand down over time in accordance with the step of block 217 a of FIG.28. This is done by pulsing the additive gas flow rate, with an “on”time duration that defines the thickness of the opaque layer(s) and an“off” time that defines the thickness of the less opaque (or nearlytransparent) layer(s). The number of pulses determines the number ofalternating opaque and non-opaque layers in the anti-reflection coating.Their optical thickness may generally correspond to a quarter wavelengthof the DSA light source. FIG. 29B is a graph illustrating the additivegas fractional composition of the total process gas in the reactorchamber as a function of time, which alternates between anabsorption-enhancing species precursor (e.g., a boron-containing gas)and a transparency-enhancing species precursor (e.g., afluorine-containing gas) in accordance with the step of block 217 b ofFIG. 28. The on-time of the absorption-enhancing additive gas flowdetermines the thickness of the opaque layers of the anti-reflectionsection of the OAL, while the on-time of the transparency-enhancingadditive gas flow determines the thickness of the transparent layers inthe anti-reflection section of the OAL. FIG. 29C is a graph illustratingthe value of a selected process parameter (such as RF bias power)affecting absorption of the deposited material as a function of time. InFIG. 29C, the process parameter value is pulsed between a low and a highvalue in accordance with the step of block 217 c of FIG. 28. This stepmay be combined with the step of either block 217 a or 217 b. In thecase of bias power, a high value produces more compressive stress in thedeposited material, making it denser and thereby enhancing itsabsorption or extinction coefficient k, while the lower value forms asub-layer with a smaller k. Other process parameters tending to affectoptical absorption characteristics of the deposited material also may bepulsed in a similar manner to enhance the effect. Such additionalprocess parameters may include chamber pressure, wafer temperature,source power, gas flow rate of the basic deposition material precursorgas (e.g., the carbon-containing gas in the case of an amorphous carbonOAL).

An OAL including an anti-reflection section formed by any of theforegoing steps is depicted in FIG. 30. The OAL, which may be anamorphous carbon layer, is formed over the wafer 251 and its thin filmstructure 252 by the low-temperature CVD process. The step of block 217of FIG. 28 is carried out during at least a portion of the CVD process,so that a section 253 a of the OAL 253 consists of alternating opaqueand non-opaque layers 253 a-1, 253 a-2, 253 a-3, 253 a-4. If thealternating layers 253 a-1 through 253 a-4 are of the appropriatethickness (e.g., a quarter wavelength of the DSA light source), then thesection 253 is an anti-reflection coating within the OAL. Alternatively,the anti-reflection section 253 a, which is shown in FIG. 30 as aninternal component of the OAL 253, may instead be a coating on the topof the remainder of the OAL 253.

While the foregoing examples concern an OAL in which the opticalabsorption is maximized, the low-temperature CVD process described abovemay be used to form an OAL or amorphous carbon layer having low opticalabsorption at the wavelength of the light source. This may beaccomplished, for example, by refraining from including or adding boronor other absorption-enhancing impurities in the OAL. In the case of apure amorphous carbon OAL, the low-temperature CVD process forms arelatively transparent layer at the wavelength (810 nm) of the GaAsdiode laser array 32 of FIG. 3. If even greater transparency (or lessopacity/absorption) is desired, then transparency-enhancing impurities(such as fluorine) may be added to the OAL either by including anappropriate precursor (e.g., fluorine-containing) gas in the CVD processor by a post-CVD ion implantation step.

FIG. 31 depicts the semiconductor wafer 40 and DSA light source 260 (ofFIGS. 1-8) performing the DSA process on the wafer to carry out the stepof block 230 of any one of FIGS. 20, 21, 24 or 28. As shown in FIG. 31,the wafer 40 is coated with the OAL layer 253 that was deposited in thelow-temperature CVD process described above. The OAL 253 has any one ormany or all of the features described above, such as, for example, anamorphous carbon basic material and absorption-enhancing features suchas absorption enhancing impurities introduced during CVD processing orduring a post-CVD ion implantation process, an anti-reflection sectionor coating, and/or an enhanced density. The DSA light source of FIG. 31includes the array of laser bars 132, the array of micro-lenslets 140,an optional interleaver 142, an optional polarization multiplexer 152, aseries of lenses 162, 164, 166, a homogenizing light pipe 170 and thefast axis focusing optics 180, 182, and a pyrometer 161, all describedearlier with reference to FIGS. 1-8. The view of FIG. 31 is along thelight source fast axis. The beam moves relative to the wafer 40 alongthe light source slow axis (transverse or perpendicular to the fastaxis).

FIG. 32 illustrates one embodiment of an integrated system for annealingsemiconductor junctions (ultra shallow junctions) in the wafer. Theintegrated system of FIG. 32 is in a “twin” configuration on a singleplatform having a common wafer handling robot or mechanism 310 on whichpairs of different tools are integrated. Specifically, the robot waferhandler 310 interfaces with a pair of input/output wafer ports 315 a,315 b, a pair of toroidal plasma source low-temperature CVD reactorchambers 320 a, 320 b of the type described above with reference to FIG.9, a pair of DSA chambers 325 a, 325 b each including a complete lightsource of the type described above with reference to FIGS. 1-8, and apair of optical absorber layer strip chambers 330 a, 330 b. FIG. 33illustrates another embodiment of an integrated system for forming andannealing semiconductor junctions and which is capable of performing allthe steps and processes described above with reference to FIGS. 20-29.The integrated system of FIG. 33 has a wafer handler 350 with waferinput/output ports or factory interfaces 355, 355′. The following toolsor reactor chambers are coupled to the wafer handler 350: a pre-ionimplant wafer cleaning chamber 360, an ultra-shallow junction dopant ionimplantation reactor 365, a post-ion implant resist strip chamber 367, atoroidal plasma source reactor 370 of the type illustrated in FIG. 9 forcarrying out the low-temperature CVD formation of the optical absorberlayer, a post-CVD ion implantation reactor 375 for implanting opticalabsorption-enhancing impurities or additives into the OAL deposited onthe wafer in the reactor 370, a DSA chamber 380 that includes the DSAlight source 260 of FIG. 31, and an OAL strip chamber 385 for performinga post-DSA OAL removal process. A wet clean chamber may be used afterthe post-ion implant resist strip chamber 367 or the OAL strip chamber385.

The pre-implant wafer cleaning reactor 360 may be a conventionalcleaning reactor, but may be another toroidal source plasma reactor ofthe type illustrated in FIG. 9 in which cleaning gases (e.g.,hydrogen-containing or oxygen-containing or fluorine-containing gases ornitrogen-containing gases, or an inert gas such as helium, neon, argonor xenon) are introduced while a plasma is generated. The dopant ionimplantation reactor 365 may be a conventional ion beam implanter or maybe a P3i reactor. Such a P3i reactor may be a toroidal source reactor ofthe type illustrated in FIG. 9 for carrying out P3i junction formationprocesses discussed earlier in this specification with reference to thepublished application by Hiroji Hanawa et al. referred to earlierherein. The post-CVD ion implantation reactor 375 may be a conventionalion beam implanter or may be a P3i reactor. Such a P3i reactor may be atoroidal source reactor of the type illustrated in FIG. 9 for carryingout P3i processes discussed earlier in this specification with referenceto the published application by Hiroji Hanawa et al. referred to earlierherein. In this case, however, the implanted species is an opticalabsorption-enhancing species precursor gas, such as a boron-containinggas, for example. The OAL strip reactor 385 may be a conventionalreactor for removing the OAL material from the wafer. If the OAL isamorphous carbon, then the strip chamber 385 employs oxygen and/ornitrogen gas and may heat the wafer and/or bias the wafer to expeditethe removal process. However, the OAL strip reactor 385 may be atoroidal plasma source reactor of the type illustrated in FIG. 9, inwhich oxygen and/or nitrogen-containing gas, hydrogen-containing gas, orfluorine-containing gas is introduced and a plasma is generated withplasma source power. The wafer may also be heated (with heated waferchuck or plasma-heated) and/or be biased to improve removal of the OALor amorphous carbon layer. For example, in a toroidal plasma sourcestrip reactor, the wafer is placed on a heated electrostatic chuck at atemperature of 250 degree C. In the first step, a gas mixture of O2, H2,N2 and NF3 flows into a toroidal plasma source reactor. RF toroidalsource power of 2 kW is applied to each of 2 toroidal plasma sources. RFbias voltage of 500V is applied to the electrostatic chuck. Afterpartially stripping the amorphous carbon layer, in the second step, agas mixture of O2, H2, N2 flows into the toroidal plasma source reactor.RF toroidal source power of 1 kW is applied to each of 2 toroidal plasmasources. RF bias voltage of 50V is applied to the electrostatic chuck.The second step is carried out until the amorphous carbon layer has beenremoved. Optionally, an optical emission line endpoint signalcorresponding to the presence or absence of carbon (or of the underlyingmaterial) in the plasma may be monitored and may optionally trigger thestrip process to end. For example, an emission line of excited CO may beused to indicate the presence of a carbon by-product in the plasma. Whenthe CO emission line signal disappears, the carbon layer has beenremoved. The strip process described above for removing the OAL layermay also be employed as a chamber cleaning process in the OAL depositionreactor (the reactor employed to deposit the carbon OAL layer) to removecarbon and other materials deposited on chamber surfaces after the waferhas been removed or before the wafer is introduced into the chamber.More generally, for a toroidal plasma reactor used to deposit anycarbon-containing layer (whether or not it has certain optical orelectrical characteristics), the above-described two-step carbon stripprocess may be employed as a chamber cleaning process before waferintroduction or after wafer removal from the chamber. For example, thiscarbon strip process may be employed as the chamber cleaning step ofblock 6141 of FIG. 19 described above.

Process Examples:

The following is a partial list of carbon precursors for the opticalabsorber layer deposition:

C H Methane 1 4 Acetylene 2 2 Ethylene 2 4 Ethane 2 6 Propylene 3 6Propane 3 8 Ethyl acetylene 4 6 1-BUTYNE 1,3-butadiene 4 6 1-butene 4 8n-butane 4 10 Pentane 5 12 Hexane 6 14 Toluene 7 8 Methyl benzene(C₆H₅CH₃

Other precursors such as fluorocarbons may be used but tend to havepoorer absorption (i.e., extinction coefficient or imaginary part of thecomplex refractive index) at the wavelength of radiation of the laserlight beam as compared with hydrocarbons. Fluorocarbons may therefore beuseful where it is desired to deposit a layer, or a portion of a layer,that is more transparent or less absorbing/opaque. Preferredfluorocarbon gases are C4F6 or C3F6. Other fluorocarbon gases includeC2F4, C2F6, C3F8, C4F8 and C5F8. Impurity examples to further enhanceoptical properties are B2H6, BF3, B5H9, PH3, PF3, AsH3, AsF5, SiH4,SiF4, GeH4, GeF4, with the hydrides generally providing betterabsorption than the dopant-fluorides. In one example, on a 300 mmsilicon wafer, C3H6 is used as a C-precursor gas at a flow rate of 600sccm, with B-precursor B2H6 at a flow rate of 20 sccm, H2 at 180 sccm,and dilution gas Ar 200 sccm at a process chamber pressure of 15 mtorr.RF toroidal source power of 2 KW (at frequency of approximately 12-14MHz) for each of two reentrant tubes in a crossed-toroidal configurationis applied. RF bias voltage (at frequency of 1-3 MHz) is ramped up to 7KV peak-to-peak from zero after several seconds, requiring about 8 KW RFbias power. The electrostatic wafer chuck is maintained in a range −20to +40C, and the wafer temperature is about 80 degrees to 140 degreesC.). For a 1-minute process time, film thickness is about 0.25 micronand “k” value is about 0.36 at laser wavelength of about 800 nm. Filmthickness is linear with deposition time, yielding about 0.75 micron in3 minutes. B-precursor B2H6 (max 10-20%) is commonly available dilutedwith H2, He, Ar or N2, as its high reactivity precludes availability at100%. While the H2 or He dilution is most preferred, Ar or N2 dilutionmay also be used. Other boron precursors may also be used. Withoutboron, the above example conditions yield a film with a “k” value ofabout 0.18 at laser wavelength of about 800 nm. N2 may be added insteadof boron: With N2 and without boron, the above example conditions yielda film with a “k” value of about 0.25 at laser wavelength of about 800nm. If lower “k” value films are desired for some other applications, H2may be added. With 200-400 sccm added H2 and without boron or N2, theabove example conditions yield a film with a “k” value of about 0.04 atlaser wavelength of about 800 nm. Alternatively or additionally,fluorine-containing gas may be added to yield a low “k” film.

Amorphous carbon films may be deposited with control of the “k” value(absorption or extinction coefficient or imaginary part of the complexrefractive index) over a wide range, while providing good step coverageover topography, free of voids, and control of film stress to improvethermal properties and avoid cracking or peeling, even when subjected tolaser annealing or conventional annealing. Chuck or wafer temperaturemay be lower to increase deposition rate without sacrificing “k” valueor other film properties. Curing at 450C for several seconds increases“k” value to about 0.36. The layer allows efficient absorption of thelaser, allowing the doped-silicon to be activated while the integrity ofthe absorber layer is maintained. The wafer surface may be taken to themelting temperature without failure of the absorber layer. Then afteranneal, the absorber layer may be stripped and cleaned in a conventionalmanner (as photoresist strip/clean process). Alternatively, the stripprocess may also be carried out back in the same or a different plasmachamber having the above-described toroidal plasma source, using oxygenor oxygen/nitrogen mixtures.

The deposition process may be multi-step (as discussed above withreference to FIGS. 24 and 28). In the above example of the foregoingparagraph, the boron-precursor may be deliberately delayed inintroduction until after an initial boron-free layer is deposition, toavoid potentially doping the wafer. A delay of 3 seconds, for example,yields a boron-free layer thickness of about 100-150 angstroms. The biasvoltage may be deliberately delayed in introduction until after aninitial source-power-only deposition process. The can be used to preventimplantation of deposition precursors into the wafer surface. These maybe used separately or together. In one embodiment, boron-precursorintroduction and bias-voltage-on are delayed 3 seconds, thenboron-precursor is added, then after an additional 3 second delay, biasvoltage is ramped up or stepped on. This reduces probability ofdeposited or implanted boron or carbon. Alternatively, N2 is added(instead of boron) after an initial delay of 3 seconds, bias-voltage isstepped on after an additional 3 second delay. In yet anotherembodiment, N2 is added (instead of boron) after an initial delay of 3seconds, bias-voltage is stepped on after an additional 3 second delay,then after 60 seconds, boron-precursor is turned on (with or without N2)for the remainder of the process. In the low temperature toroidal plasmaCVD process for depositing the amorphous carbon film as an opticalabsorber at some wavelength of interest (e.g., 810 nm), there is asynergistic benefit of adding (1) boron (i.e., B2H6) plus (2) N2 orother form of nitrogen to the basic amorphous carbon precursorhydrocarbon gas (i.e., C3H6). Thermal stability of the deposited carbonlayer is improved at 450 degrees C. and especially higher temperatures.Specifically, the deposited amorphous carbon layer may be laser heatedto or above melting point of silicon without delamination of thedeposited layer, or peeling, etc. This feature actually reduces thethreshold wafer voltage or threshold ion energy typically required toavoid delamination or peeling. The foregoing feature of combining boronand nitrogen additives in the hydrocarbon gas may be employed whendepositing an optically-absorbing amorphous carbon layer, and may alsobe employed for depositing a carbon layer that is not an opticalabsorber. In another example, on a 300 mm silicon wafer, Ar isintroduced by itself at a flow rate of 800 sccm and pressure of 30 mtorrto initiate the plasma with the application of RF toroidal source powerof 1 KW (at frequency of approximately 12-14 MHz) for each of tworeentrant tubes in a crossed-toroidal configuration. Following theplasma initiation step, the throttle valve is adjusted to reduce thechamber pressure to 15 mtorr and this is maintained through theremainder of the deposition process. Then, the Ar flow is reduced to 200sccm and C3H6 is introduced as a C-precursor gas at a flow rate of 600sccm, and the toroidal source power level is increased to 2 kW per tubefor a period of 3 seconds to deposit an initial interface layer.(Toroidal source power level is maintained at 2 kW per tube for theremainder of the deposition process.) Then N2 is introduced at a flowrate of 333 sccm and RF bias voltage (at frequency of 1-3 MHz) is rampedup to 7 KV peak-to-peak from zero or a low initial value after severalseconds, requiring about 8 KW RF bias power. After about 40 seconds,B2H6 is introduced at a flow rate of 20 sccm with a hydrogen dilutiongas at a flow rate of 180 sccm and the N2 flow is (optionally)discontinued. This step is carried out for 140 seconds. During theentire run, the electrostatic wafer chuck is maintained in a range −20to +40C, and the wafer temperature is about 80 degrees to 140 degreesC.). For the approximately 3-minute total process time, film thicknessis about 0.75 micron and “k” value is about 0.36 at laser wavelength ofabout 800 nm. The film has excellent thermal stability and conformality,and has minimum implantation damage of the underlying wafer surface.And, it is strippable (with or without anneal) in either the toroidalstrip chamber previously described earlier, or in a conventionaldownstream radical strip process chamber at a wafer temperature of 250degrees C., using a mixture of nitrogen and oxygen with less that 10%CF4. The CF4 or alternative fluorine source may be stopped after theinitial top boron-containing layer has been stripped (fluorine oralternatively hydrogen helps remove the boron), after which conventionalnitrogen and oxygen are effective in removing the remaining filmthickness with minimum damage to the underlying wafer surface.

While the invention has been described in detail by specific referenceto preferred embodiments, it is understood that variations andmodifications thereof may be made without departing from the true spiritand scope of the invention.

1. A method of depositing a carbon layer on a workpiece, comprising:placing the workpiece in a reactor chamber; introducing acarbon-containing process gas into the chamber; generating a reentranttoroidal RF plasma current in a reentrant path that indludes a processzone overlying the workpiece by coupling plasma RF source power to anexternal portion of said reentrant path; coupling RF plasma bias poweror bias voltage to the workpiece; and enhancing optical absorption ofthe deposited carbon layer by heating the carbon layer followingcompletion of its deposition.
 2. The method of claim 1 wherein the stepof introducing the carbon-containing process gas comprises introducingthe process gas through a gas distribution plate overlying the workpieceand underlying the external portion of the reentrant path.
 3. The methodof claim 1 wherein said process gas comprises a hydrogen-carbon chemicalspecies.
 4. A method of depositing a carbon layer on a workpiece,comprising: placing the workpiece in a reactor chamber; introducing acarbon-containing process gas into the chamber; generating a reentranttoroidal RF plasma current in a reentrant path that includes a processzone overlying the workpiece by coupling plasma RF source power to anexternal portion of said reentrant path; coupling RF plasma bias poweror bias voltage to the workpiece; and setting conductivity of the carbonlayer between insulative and semiconductive by at least one of: (1)adjusting the ion bombardment energy at the wafer surface, (2) adjustingthe workpiece temperature, (3) selecting the hydrogencarbon gas speciesof the process gas in accordance with a hydrogen-carbon ratio of thegas, (4) diluting the process gas with hydrogen, (5) diluting theprocess gas with an inert gas such as helium, neon, argon or xenon, (6)adjusting the flux of energetic ions at the wafer surface relative tothe flux of carboncontaining radical species to the wafer surface, (7)adding to the process gas a precursor additive gas of one of: (a) asemi-conductivity-enhancing species, (b) a resistivity-enhancingspecies; (8) implanting in the deposited carbon layer one of: (a) asemiconductivity-enhancing species, (b) a resistivity-enhancing species.5. A method of depositing a carbon layer on a workpiece, comprising:placing the workpiece in a reactor chamber; introducing acarbon-containing process gas into the chamber; generating a reentranttoroidal RF plasma current in a reentrant path that includes a processzone overlying the workpiece by coupling plasma RF source power to anexternal portion of said reentrant path; coupling RF plasma bias poweror bias voltage to the workpiece; and setting the transparency oropacity of the carbon layer by at least one of: (1) adjusting the ionbombardment energy at the wafer surface, (2) adjusting the workpiecetemperature, (3) selecting the hydrogencarbon gas species of the processgas in accordance with a hydrogen-carbon ratio of the gas, (4) dilutingthe process gas with hydrogen, (5) diluting the process gas with aninert gas such as helium, neon, argon or xenon, (6) adjusting the fluxof energetic ions at the wafer surface relative to the flux ofcarbon-containing radical species to the wafer surface, (7) adding tothe process gas a precursor additive gas of one of: (a) anabsorption-enhancing species, (b) a transparency-enhancing species; (8)implanting in the deposited carbon layer one of: (a) anabsorption-enhancing species, (b) a transparency-enhancing species. 6.The method of claim 5 wherein the absorption-enhancing species is one ofboron, nitrogen, sulfur.
 7. The method of claim 5 wherein thetransparency-enhancing species is fluorine.
 8. The method of claim 1further comprising enhancing the adhesion of the deposited carbon layerto the underlying workpiece by setting the bias power or bias voltage toa sufficiently high level.
 9. The method of claim 1 further comprisingenhancing the adhesion of the deposited carbon layer to the underlyingworkpiece by increasing the level of the bias power.
 10. The method ofclaim 1 further comprising setting stress within the deposited carbonlayer to one of compressive stress and tensile stress by adjusting thebias power or bias voltage.
 11. The method of claim 1 further comprisingincreasing compressive stress in the deposited carbon layer byincreasing said bias power or bias voltage.
 12. The method of claim 1further comprising controlling the conformality of the deposited carbonlayer by setting the level of said RF plasma source power.
 13. Themethod of claim 1 wherein the carbon layer is heated to about 400degrees C.
 14. The method of claim 1 wherein said process gas is afluorocarbon gas.
 15. The method of claim 4 wherein: the step ofadjusting the energy of ions incident on the workpiece comprises atleast one of: adjusting the bias power or bias voltage, adjusting thepressure inside the chamber; the step of adjusting the flux of ionsincident on the wafer comprises at least one of: adjusting the sourcepower; adjusting the pressure inside the chamber, adjusting the dilutiongas flow rate.
 16. The method of claim 5 wherein: the step of adjustingthe energy of ions incident on the workpiece comprises at least one of:adjusting the bias power or bias voltage, adjusting the pressure insidethe chamber; the step of adjusting the flux of ions incident on thewafer comprises at least one of: adjusting the source power; adjustingthe pressure inside the chamber, adjusting the dilution gas flow rate.17. A method of depositing a carbon layer on a workpiece, comprising:placing the workpiece in a reactor chamber; introducing acarbon-containing process gas into the chamber ; generating a reentranttoroidal RF plasma current in a reentrant path that includes a processzone overlying the workpiece by coupling plasma RF source power to anexternal portion of said reentrant path; coupling RF plasma bias poweror bias voltage to the workpiece; and including a layer-enhancingadditive gas that enhances thermal properties of the deposited carbonlayer.
 18. The method of claim 17 wherein said layer-enhancing additivegas comprises a combination of a boron-containing gas and anitrogen-containing gas.
 19. The method of claim 18 wherein said processgas comprises a hydrocarbon gas, said boron-containing gas comprisesB2H6 and said nitrogen-containing gas comprises N2.